Method of operating an in-line legged robot vehicle

ABSTRACT

A single track in-line legged vehicle is controlled to coordinate movement along a desired single-track trajectory by causing each in-line leg to selectively perform a stance-to-flight phase, a flight phase, a flight-to-stance phase, and a stance phase. During the stance-to-flight phase, reaction forces and torques between a foot and the ground are unloaded to lift the foot off the ground. During the flight phase, a foot moves in the same general direction and at a generally faster rate as a major direction of motion of the vehicle body. During the flight-to-stance phase, foot positioning is controlled to place a foot on the ground according to the desired single-track trajectory. During the stance phase, foot-to-ground interaction develops reaction forces and torques that are transferred from the foot through the corresponding in-line leg to propel, torque, and stabilize the body in the x, y, z, pitch, roll, and yaw axes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/052,821, filed Mar. 21, 2011, entitled “IN-LINE LEGGED ROBOT VEHICLEAND METHOD FOR OPERATING”, now allowed, which claims the benefit of U.S.Provisional Patent Application No. 61/316,213 filed on Mar. 22, 2010,the disclosures of which are fully incorporated herewith by reference.

FIELD OF THE INVENTION

The present invention relates to a legged mobile robot and, moreparticularly, to a legged mobile robot having a plurality of legsarranged in a narrow profile to walk and maneuver along paths by placingsuccessive footfalls in a generally single-track or inline fashion.Furthermore, the invention relates to an automatic system for sensingand preventing turnover of single-track legged mobile robots whileenabling normal riding techniques in all but out of control situations.

BACKGROUND OF THE INVENTION

Prior-art legged vehicles, especially those adapted for moving overrough or uneven terrain have been proposed. The terms vehicle, walkingmachine, and robot are to be construed broadly and includes any means oftransportation, whether merely of itself or of objects other thanitself. As early as 1898, H. G. Wells described a fictional 100 foottall, three-legged walking machine in his science fiction novellaentitled “War of the Worlds”, and it was first drawn by Warwick Globecirca 1898. In the drawing, the three legs are symmetrically positionedin a triangular pattern to form a tripod stance. About that same timeMuybridge used stop-motion photography to study legged locomotion inanimals (Muybridge 1899) and later humans (Muybridge 1901). His workprovided a method for structuring classical quadruped and biped walkinggaits in biologically-inspired legged machines.

Further developments in legged locomotion occurred in the 1960's whenresearch progressed from observation to modeling. It was believed thatlegged locomotion would increase the speed of vehicles traversingunimproved or rough terrain by a factor of 10×. That is, animals wereobserved traversing rough terrain at 35 mph while wheeled vehiclesmanaged only 3-5 mph. Additionally, legged locomotion promised betterisolation from terrain irregularities. Researchers have investigatedfour-bar linkages, cam linkages, pantograph mechanisms, and so on, andhave built a walking machine with four rectangular frames, controlled bya set of double-rocker linkages, using non-circular gears to produceuniform walking velocity. Additionally, a hexapod and an eight-leggedwalking machine were developed for lunar rover application. Both walkingmachines were controlled using mechanical, cam-linkage mechanisms. Thesedesigns employed statically stable, symmetric walking gaits, andrequired moving pairs of opposing legs to keep the body in staticequilibrium at all times. These gaits have also been modeledmathematically and diagrammatically, wherein fundamental terminology wasdefined, such as stance, swing, stride length, duty factor, phase,stability, and so on. For example, a leg is either on the ground, calledthe stance state or phase, or in the air, called the swing or flightstate or phase, and a stride measures the distance the body moves in onestance-to-swing locomotion cycle. The aforementioned prior art vehiclesare generally very large, bulky, and cumbersome, and such prior artlegged vehicles generally move slower than comparable wheeled vehicles.This highly limits their usefulness.

Further developments in legged walking machines used a computer tocontrol the motion of an eight degrees-of-freedom (DOF) quadruped. Thequadruped had two degrees-of-freedom (DOF) for each leg, one DOF at thehip and one DOF at the knee, with independent electromechanicalactuators at each leg joint. Using the computer to coordinate ororchestrate the leg joint movements, it demonstrated the classicalquadruped walk and trot gaits. Also about that time, General ElectricCorporation built a 3000 pound, hydraulically-actuated quadruped thathad three DOF per leg, two DOF at the hip and one DOF at the knee. Theirquadruped was controlled by a human operator, and it demonstrated thatlegged machines can move effectively on rough terrain and climb overobstacles, with a human providing control and sensing. Such efforts ledto the development of various theories and algorithms for coordinatingleg movements in bipeds, quadrupeds, hexapods, and other symmetriclegged walking machines to walk over rough terrain, evaluate footholds,and walk outdoors on various types of terrain. In 1968, researchers atOhio State University proved mathematically that there is an optimalgait for a quadruped that maximizes the longitudinal stability margin.They built a 300 pound hexapod that used force sensors, gyroscopes,proximity sensors, and a camera system to study control algorithms forlegged walking machines. Finally, various experiments have beenperformed on quadruped robots to study walking gaits when one leg isinoperative. In such work, two legs are in-line and the third leg isoffset with one of the in-line legs, as in a right-angle triangleorientation, and the two offset legs walk in a predominately bipedalgait with the single in-line leg implementing a hopping motion.

Further developments in legged machines were made to investigateunstable or dynamic legged machines by studying balance of one, two, andfour-leg hopping machines. Legged vehicles with less than six legsgenerally require some degree of dynamic balance to stabilize the bodyagainst roll and pitch. The danger of overturning is increased when thelegged vehicle is carrying at least one rider or passenger because therider may make moves which can upset the control system, destroying thenormal lateral balance of the legged vehicle and thus causingoverturning of the legged vehicle. Prior art stabilization techniques,for example, involve the development of a factor of safety with regardto keeping the center of gravity within the center of pressure of thelegs, using a large passive gyro and its precessional momentum tocontrol body pitch and roll, or using retractable outrigger wheels tocatch the fall. Such prior art are unsuitable both in terms of weightand use in rugged and uneven terrain. A one-legged hopping machine wasinvestigated. The leg hopping machine was statically unstable and wouldfall down without constant placement-thrust movement of the foot tocompensate for instability. The one-legged hopping machine was modeledas an inverted pendulum and decomposed control into three separateelements: 1) supporting the body by controlling the vertical hoppingheight, 2) positioning the feet in key locations on each step usingsymmetry principles to keep the robots balanced, and 3) controlling thebody attitude by controlling hip torque during the stance phase suchthat the dynamic momentum state of the body is estimated ahead in timeto calculate the future foot placement and thrust needed to developcomplementary dynamic momentum and achieve a desired hopping height,running velocity, and body attitude. This seminal control systemdemonstrated dynamic re-stabilization against overturning when subjectto unexpected forces that destroy the normal lateral balance of thevehicle, thus cause overturning, or when moving on unstable or slipperysurfaces, the latter conditions causing foot slip to occur and thuscause overturning. The concept of a virtual leg was developed formodeling dynamic gaits, such as the trot and the pace gaits, wherebysymmetric multi-leg machines are modeled as one-leg hopping machines. Inother words, for dynamic gaits a biped is modeled as a one-leg machinethat alternates the use of left and right legs for support, a quadrupedis an extension of a biped when pairs of legs (diagonal pairs for thetrot and lateral pairs for the pace) move together and can be modeled asa single virtual leg, and so on. However, this research did not includethe bounding gait, where front and rear pairs of legs are movedtogether, in the same class as the aforementioned trot and pace gaitsbecause it requires using a multi-segmented body to position the virtualfoot under the center of mass to provide support, given a body lengthgreater than the leg reach. About the same time, others realized astable bounding gait for quadruped robots by controlling hip torqueduring the stance period using a quasi-static slip control algorithm. Itwas also shown that a simplified control rule stabilizes running withoutvelocity and trunk angle feedback.

Further developments in legged machines have come about because ofadvances in high-accuracy, high-pressure servo hydraulics combined withreal-time low-level control systems. Such legged actuator systems servopositions and forces at the actuated joints to regulate ground reactionforces, maintain support, position, and traction. For example, BostonDynamics Company built and demonstrated the BigDog quadruped robot. TheBigDog quadruped robot has multi jointed legs adapted for limitedoscillatory movement and exhibits a variety of locomotion behaviors:stand up, squat down, walk with a crawling gait that lifts just one legat a time, walk with a trotting gait that lifts diagonal legs in pairs,trot with a running gait that includes a flight phase, and bound in aspecial gallop gait. For example, BigDog walks with a dynamicallybalanced trot gait. It balances using an estimate of its lateralvelocity and acceleration, determined from the sensed behavior of thelegs during stance combined with the inertial sensors. A high-levelcontrol system coordinates behaviors of the legs to regulate thevelocity, attitude, and altitude of the body during locomotion. Forexample, the BigDog control system coordinates the kinematic and groundreaction forces of the robot while responding to basic posturalcommands. Load is distributed over the stance legs to optimize theload-carrying ability. The vertical loading across limbs is kept asequal as possible while individual legs are encouraged to generateground reactions towards the hips, thus lowering required joint torquesand actuator efforts. A gait coordination algorithm, responsible forinter-leg communication, initiates leg stance transitions to produce astable gait. A virtual leg model coordinates the legs. The controlsystem adapts to terrain changes through terrain sensing and posturecontrol.

Further developments in legged machines have been realized byimprovements in low-power, high computational throughput, self-containedcomputer systems capable of receiving sensory input, calculating thesystem and leg kinematics, and controlling each leg joint. For example,a novel tripod robot was designed with omnidirectional legs and bodysuch that the body rotates in the pitch and yaw axis allowing a leg toswing under the body to afford pairs of legs to contact the groundsimultaneously. For example, a machine vision algorithm developed bythis inventor uses visual data to find the gravity vector in man-madeenvironments, a form of dead reckoning used for balance.

SUMMARY OF THE INVENTION

A vehicle with legs can go where wheeled or tracked vehicles cannot go.Legged vehicles have improved mobility over rugged terrain with unstablefootholds, such as mountain slopes and piles of rubble. Legged vehicleschoose discrete, optimal foot placement and vary the length of the legwith respect to the body. Additionally, legged vehicles can bound, leap,or jump over areas of ground that do not have a continuous path ofsupport or closely spaced footholds. Moreover, legged vehicles are ableto move in man-made or cultural environments, traversing obstacles suchas curbs, stairs, and narrow passageways. With respect to wheeledvehicles, legged vehicles reduce body motion. This characteristic isespecially well suited to the comfort of a rider or passenger.

The term robot is to be construed broadly and includes any means ofvehicular transportation, whether merely of itself or of objects otherthan itself, relating to a device and method that works autonomously orsemi-autonomously whereas the term machine or vehicle, as in themotorcycle or bicycle, relates to an operated device. The robot/vehicleof the present invention takes people places they normally cannot go. Itis designed with a narrow profile to walk and maneuver along narrowtrails and paths, such as for example horse trails found in parks andwilderness areas. Hopping, bounding, leaping, and jumping enable it totraverse terrain that is too difficult for comparable wheeled machines.Because it has legs like a horse, it does not damage the environmentlike bicycles, motorcycles, and 4×4 vehicles do. It brings back thethrill of trail riding to improve human health and emotionaldevelopment. It may also be used as a “pack mule” to carry heavy loadsand accompany hikers.

Compared to a quadruped or four-legged mobile robot, the presentinvention uses 3/4 fewer parts, and would thus have higher reliabilityand cost less to manufacture. Like the quadruped, the single trackdesign is a statically stable design, because the legs can be positionedin a tripod stance. Unlike biped or two-legged mobile robots that mustsimultaneously maintain balance in both the pitch and roll directions,the robot's/vehicle's balance is controlled in the roll direction.Further, a three-legged design enables the present invention to maintain(or regain) stability of balance at rest and during locomotion, byrepeating intervals of dynamic momentum followed by the stable tripodstance. The present invention has the following key features, functions,and benefits:

-   -   Bounding, leaping, or jumping over areas of ground that do not        have a continuous path of support or closely spaced footholds    -   Carries rider, passenger, and/or cargo    -   High-speed legged locomotion—Unlike biped and quadruped designs,        the tri-leg gate repeats intervals of the tripod stance for        stability of balance    -   High-speed turns—Like two-wheeled motorcycles, the legged mobile        robot executes a single-track turn by leaning the body into the        turn to develop a torque about the roll axis to counteract the        outward centripetal force    -   Improved ride quality—Single track legs reduce body motion        compared to biped and quadruped designs and wheels in rough        terrain; this characteristic is especially well suited to the        comfort of a rider, passenger, and/or fragile cargo    -   Light weight, have fewer mechanical components, increased        reliability, high energy efficiency, and fast acceleration        compared to quadruped robots    -   Low environmental impact—The feet of legged mobile robots are        stationary with respect to footholds during the support period    -   Multiple terrain capability—Interchangeable feet for different        conditions, e.g., paved roads, snow (skis), beaches (sand), etc.    -   Operator interface—Communicates status through an operator        interface    -   Robotic control system—Relies on riders for high-level control        and stability, but also allows semi-autonomous behavior, such as        self-guided, GPS-based tours    -   Self-recovery from slips and falls—Able to place a leg in the        direction of fall to regain support during operation/motion    -   Stable stance—Unlike two-wheeled motorcycles, three legs may be        positioned in a tripod stance to enable the legged robot to        achieve stability of balance without motion    -   Traverses man-made obstacles such as curbs, stairs, and narrow        passageways—legged vehicles chooses optimal foot placement by        varying the length of the leg.

Like wheeled motorcycles and bicycles, the legged mobile robot of thepresent invention executes a single-track turn by leaning the body intothe turn, thus developing a torque about the roll axis to counteract theoutward centripetal force. The single track or in-line legged mobilerobot is inherently stable along the length of the body or major axis ofmotion. The control strategy decouples the leg positioning along thelength of the body or major axis of motion and the leg positioning alongthe width of the body or normal to major axis of motion. That is, leggedvehicles heretofore must simultaneously maintain stability of balance inthe pitch and roll direction. The single track or in-line legged mobilerobot controls stability of balance in the roll direction and (for themost part) not in the pitch direction. Like a quadruped, yaw iscontrolled by developing torque about any two legs during the stancephase. This device and method drastically simplifies control for manysingle track or in-line legged gates and modes of operation.Furthermore, the control system senses and prevents turnover of singletrack legged mobile robots while enabling normal riding techniques inall but out of control situations.

It has not heretofore been possible to realize a multi-legged vehicle,i.e. robot or machine, having a plurality of legs arranged in aminimally narrow profile to place successive footfalls in apredominately single-track or in-line fashion, similar in form andfunction to motorcycles and bicycles. In off-road environments, such asparks and wilderness areas, single track vehicles, such as motorcyclesand bicycles, exhibit superior maneuverability and deploymentperformance in comparison to double track vehicles, such as automobilesand tanks Moreover, single track vehicles are typically lighter inweight, have fewer mechanical components, increased reliability, higherenergy efficiency, and faster acceleration and deceleration. Furtherwhile the aforementioned prior art legged vehicles provide means forimplementing various static and dynamic walking gaits, they do notdisclose a device or method for single track or in-line multi-leggedstatic and dynamic gaits.

According to the present invention, there is provided a single track orin-line multi-legged mobile robot which achieves the desired form andfunction of the motorcycle or bicycle but with the added benefit of legsand full or partial robotic control. The term robot relates to a deviceand method that works autonomously or semi-autonomously whereas the termmachine or vehicle, as in the motorcycle or bicycle, relates to anoperated device.

Briefly, a single track or in-line multi-legged mobile robot may beconstructed in accordance with the teachings of the present inventioncomprises a device and method:

a body and three legs mounted on the body in-line with the length of thebody;

at least three legs comprising a minimally narrow profile so that as avehicle it can maneuver where prior art vehicles previously could notgo, such as walking along a narrow trail or path or through a door;

each leg is connected to a single or multi-segmented body that isgenerally longer than it is wider;

the body length establishes the major direction of motion, such asforward and backward motion;

each of the at least three legs are spatially arranged at the hip to begenerally in-line with the major direction of motion;

each of the at least three legs has at least three degrees of freedom(DOF), such as pitch and roll at the hip and extension and retraction ofthe foot, to position the foot anywhere within a three dimensionalvolume;

the at least three legs combine to form three spatial volumes for footplacement that is spatially arranged to be generally in-line with themajor direction of motion;

the at least three spatial volumes overlap along the major direction ofmotion;

the at least three legs have sufficient reach in length, width, andheight to afford the three feet to be spatially positioned 1) in atriangular (tripedal) pattern to keep the body in static equilibrium atrest, 2) in any manner of patterns to provide locomotion and dynamicattitude stabilization, and 3) for omnidirectional motion.

A control system is used to coordinate and control the leggedvehicle/robot, and may includes one or more central processing units(CPU) and one or more memory components. The memory components mayinclude one or more memory modules, such as Random Access Memory (RAM)modules, Read Only Memory (ROM) modules, Dynamic Random Access Memory(DRAM) modules, and any other suitable memory modules. The controlsystem may also include a plurality of input/output (I/O) componentsthat may include a variety of known I/O devices, including networkconnections, video and graphics cards, disk drives or othercomputer-readable media drives, displays, or any other suitable I/Omodules. One or more data busses may operatively couple the CPU, thememory component, and the I/O component. The control system may beoperatively coupled to a control component having a data display/monitorand a command/control input device (e.g. a keyboard, an audio-visualinput device, handlebars, foot pegs, pressure pads, etc . . . ).

In one aspect, a machine-readable medium may be used to store a set ofmachine-readable instructions (e.g. a computer program or softwareproduct) into the data acquisition and control system 120, wherein themachine-readable instructions embody a method of performing one or moregaits with a legged robot/vehicle/machine in accordance with the presentinvention. The machine-readable medium may be any type of medium whichcan store data that is readable by the control system, including, forexample, a floppy disk, CD ROM, optical storage disk, magnetic tape,flash memory card, digital video disk, RAM, ROM, or any other suitablestorage medium. The machine-readable medium, or the instructions storedthereon, may be temporarily or permanently installed in any desiredcomponent of the control system, including, for example, the I/Ocomponent, the memory component, and in one or more other portions ofthe control system and the control component. Alternately, themachine-readable instructions may be implemented directly into one ormore components of the control system and the control component, withoutthe assistance of the machine-readable medium.

In accordance with a first major embodiment of the invention, a leggedvehicle includes a frame, wherein the frame includes a major axiscorresponding to and generally parallel to a forward/backward directionof travel; a plurality of jointed leg mechanisms attached to the frame,one behind the other, wherein each leg is attached at its proximal endat one or more discrete attachment points, wherein the attachment pointsare arranged substantially parallel to the major axis of the frame andthe forward/backward direction of travel, each of the legs includingactuators attached between the legs and the frame and between adjacentleg members, said legs being actuated for movement of a distal end inthree dimensions; a control system in communication with the legmechanisms and receiving sensed data to determine possible future statesof the legged vehicle and to coordinate movements of the leg mechanismsand frame, and movement of the legged vehicle in three dimensions overthe ground; and a power source connected to and driving the controlsystem components and the plurality of actuators which drive the legs,wherein forward/backward movement of the legged vehicle is according toapproximately single track foot placement. The term ‘single track’ shallbe interpreted as referring to the general narrowness of thefoot-placement patterns along a straight or curved path.

Such an arrangement, wherein the legs are attached to the frameone-behind-the other (in-line), provides numerous advantages inmobility, including the ability to travel through narrow passages, suchas doorways, and along narrow paths, such as single-track trails, wheretraditional vehicles would be unable to go.

According to a first aspect of the invention, the legged vehicleincludes three legs. Three in-line legs provide an advantage of inherentstability along the pitch axis, which is generally parallel with themajor axis of the body and major direction of travel. This means thatmost of the stability process can be directed to a roll axis(side-to-side) and perpendicular to the pitch axis.

According to a further aspect of the invention, the legged vehicleincludes more than three legs. This arrangement provides greaterstability in the pitch axis, and provides multiple options for possiblefootholds while in motion, and also provides options for not placing afoot down over unstable terrain, and instead relying on dynamicstability and the remaining legs to traverse the terrain.

According to a further aspect of the invention, each of the plurality oflegs includes a foot at the distal end. Each of the feet of the leggedvehicle may include at least one of, or one or more of, plates, skids,spikes, wheels, skates, skies, slides, floats, hydroplanes, and fingers.Different combinations of the different foot-types may be used toaccommodate different types of terrain. Accordingly, different gaits maybe used according to the combination of foot-type and terrain. Thisbrings tremendous flexibility to the vehicle.

According to a further aspect of the invention, the legged vehicleincludes a single-piece frame. This simplifies the gaits and anynecessary programming to traversing terrain.

According to a further aspect of the invention, the legged vehicleincludes a frame which is jointed and includes two or more segments,each segment having a major axis corresponding to and generally parallelto a forward/backward direction of travel. The articulated frameprovides an advantage in flexibility, which extends the ranges of motionof each of the legs, particularly the front-most and rear-most legs.With proper coordination, a much faster, more natural gait can be usedto quickly traverse even the most challenging terrain.

According to a further aspect of the invention, control of movement ofthe frame and leg-positioning along the major axis corresponding to thepitch axis is decoupled from the movement of the frame andleg-positioning normal to the major axis and corresponding to the rollaxis. In this manner, the legged vehicle is operated much like amotorcycle wherein the pitch axis is responsive to the terrain and theroll axis is responsive to the rider and/or control system.

According to a further aspect of the invention, at least oneaccelerometer and at least one gyroscope mounted on the frame and incommunication with the control system, the control system receivingsensed data from the at least one accelerometer and at least onegyroscope to sense velocity, acceleration, attitude, and gravitationalforces. In a preferred embodiment the at least one accelerometer and theat least one gyroscope are mounted on the frame and sensing velocity,acceleration, attitude, and gravitational forces normal to the length ofthe body and the major axis and sense the roll condition. Additionalsensing including the pitch, yaw, x, y, and z axes may be required foromni-directional guidance, navigation and control.

According to a further aspect of the invention, the control system ofthe legged vehicle further includes at least one accelerometer and atleast one gyroscope mounted on the frame and in communication with thecontrol system and sensing velocity, acceleration, orientation, andgravitational forces, the control system receiving sensed data from theat least one accelerometer and the at least one gyroscope, wherein thesensed pitch angle velocity, acceleration, and orientation from theaccelerometer and gyroscope which are along the length of the body andcorresponding generally to the major axis is decoupled from the sensedroll angle velocity, acceleration, and orientation which are normal tothe length of the body and the major axis and generally parallel to theground when the legged vehicle is in an upright position.

The decoupling of these aspects of the control system, significantlyreduces the computing and processing capacity necessary about the pitchaxis, and permits greater flexibility of the legged vehicle's movements.

According to a further aspect of the invention, each leg mechanismincludes position-measuring components providing feedback to the controlsystem. These position-measuring components provide informationregarding relative or absolute leg position to the control system. Suchinformation provides the advantage of more-accurate leg-movementcorrections based upon a comparison, within the control system, ofcommanded or desired leg placement in comparison to actual legplacement.

According to a further aspect of the invention, each leg mechanismincludes force-measuring components providing feedback to the controlsystem. These components provide numerous advantages, including accuratedetermination of the loaded weight of the vehicle, accuratedetermination of the leg energy required, via one or more actuators, toperform a desired maneuver, such as straight-line walking, and accuratemeasurements of forces experienced at each leg and through the frame.This permits the control system to compensate according to the desirestrajectory.

According to a further aspect of the invention, each leg mechanismincludes torque-measuring components providing feedback to the controlsystem. These components provide numerous advantages, including accuratedetermination of the loaded weight of the vehicle, accuratedetermination of the leg energy required, via one or more actuators, toperform a desired maneuver, such as straight-line walking, and accuratemeasurements of torques experienced at each leg and through the frame.This permits the control system to compensate according to the desiredtrajectory.

According to a further aspect of the invention, legged movement of thevehicle is according to a gait model, wherein at least one gait model isstored in the read-only memory of the control unit. Such an embodiment,for example, may also include neural networks and the like where one ormore gait models are implicitly stored in the structure of the neuralnetwork. For example, gait models may include periodic gaits, such asthe wave gait, the equal phase gait, the backward wave gait, thebackward equal phase gait, the dexterous periodic gate, the continuousfollow-the-leader gait, and the shuffle gait, and non-periodic gaits,such as the discontinuous follow-the-leader gait, the large obstaclegait, the precision footing gait, the free gait, the vertical stepcrossing gait, the climbing gait (an example of which is illustrated inFIGS. 9-28), the shuffle gait, and the isolated wall crossing gait, toname but a few.

According to another aspect of the invention, the control system furthercomprises an omni-directional guidance, navigation, and controlalgorithm.

According to a further aspect of the invention, the forward velocity andbody height parameters are adapted for the at least one gait model usingsensed or a priori ground terrain data.

According to a further aspect of the invention, the movement range foreach of the legs defines a working envelope, each of the feet havingsufficient reach and movement range in length, width and height,relative to the frame, (1) to position two feet perpendicular to themajor axis of the frame, with one foot positioned to the left of and oneto the right of the projected center of gravity of the frame to form agenerally bipedal stance along the major axis of the frame to provide adegree of stability in the roll axis, and (2) in addition to theplacement of the first two feet, to displace a third foot into aposition parallel to the major axis of the frame, either to the front orthe rear with respect to the other feet, to form a generally tripedalstance about the projected center of gravity (center of pressure) of theframe to provide a period of stability in both the pitch and roll axes.

According to a further aspect of the invention, the movement range foreach of the legs provides range-of-motion overlap in length, width andheight of the working envelopes of each adjacent foot, including anyfoot in front of and behind each foot. This provides a tremendous amountof flexibility in achieving temporary stability while in motion and whenutilizing dynamic stability, and permits a great range of possible legpositions which are necessary when traversing difficult terrain.

According to a further aspect of the invention, the feet of two adjacentlegs, one in front of and one behind the other, are positionableside-by-side on a center of pressure line generally perpendicular to theframe and perpendicular to the major axis of motion to achieve a bipedalstance. This ability permits the frame to be positioned so as to bring azero-moment line of the legged vehicle in coincidence with the center ofpressure line, which allows the other legs of the legged vehicle to beraised off the ground, at least temporarily.

According to a further aspect of the invention, the control unit has oris in communication with an operator interface, which is incommunication with the control system, the control system receivingsensed data from the operator. This arrangement allows the advantage ofremotely-directed control of the legged vehicle, and allows arider/operator to control the legged vehicle.

According to another aspect of the invention, the operator interfacecomponents provide at least steering angle, throttle and braking inputsinto the control system. In this fashion, the legged vehicle iscontrolled by an operator in a manner similar to that of controlling amotorcycle, but with the benefit of discrete foot placement.

According to a further aspect of the invention, inputs to the operatorinterface control stability of balance in the roll axis. In other words,the operator's vestibular system may provide the function of theaccelerometer and gyroscope to sense the roll condition and control theroll of the legged vehicle through the control system and its footplacement, thusly.

According to another embodiment of the invention, a method of operatinga legged vehicle including a frame, wherein the frame includes a majoraxis corresponding to and generally parallel to a forward/backwarddirection of travel; a plurality of jointed leg mechanisms attached tothe frame, one behind the other, wherein each leg is attached at itsproximal end at one or more discrete attachment points, wherein theattachment points are arranged substantially parallel to the major axisof the frame and the forward/backward direction of travel, each of thelegs including actuators attached between the legs and the frame andbetween adjacent leg members, said legs being actuated for movement of adistal end in three dimensions; a control system in communication withthe leg mechanisms and receiving sensed data to determine possiblefuture states of the legged vehicle and to coordinate movements of theleg mechanisms and frame, and movement of the legged vehicle in threedimensions over the ground; and a power source connected to and drivingthe control system components and the plurality of actuators which drivethe legs, wherein forward/backward movement of the legged vehicle isaccording to approximately single track foot placement, the methodcomprising the steps of:

-   -   developing reaction forces, torques, and thrusts in a stance        phase wherein leg/foot-to-ground interaction is transferred        through the leg to stabilize the frame in the pitch, roll, and        yaw axes and to propel the frame in the x, y, and z axes,        respectively, the foot/distal end of the leg being generally        stationary with respect to the ground during the stance phase        and moving generally opposite to the major direction of frame        motion, of a monopedal stance, a bipedal stance and a tripedal        stance, according to the control system;    -   unloading reaction forces through the leg/foot in a        stance-to-flight phase wherein the foot is lifted off the        ground, controlling leg velocities, according to the control        system;    -   repositioning the leg/foot in a flight phase wherein the distal        end of the leg/foot is moved generally in the same direction as        the frame and generally at a faster rate, relative to the        ground, as the major direction of frame motion, controlling foot        placement and leg movement to maintain an upright posture and        meet foot placement constraints and desired trajectory        requirements for the frame and legged vehicle, according to the        control system; and    -   placing the leg/foot to the ground and developing reaction        forces, torques, and thrusts in a flight-to-stance phase;    -   wherein movement of each leg includes each of the four phases        for each leg.

According to a further aspect of the invention, the method of operatingthe legged vehicle further comprises:

-   -   during the flight phase for at least one leg, controlling leg        movement, torque, extension velocity and retraction to use the        mass of the at least one leg to impart forces and torques to the        frame in at least one dimension or axis.

According to a further aspect of the invention, the method of operatingthe legged vehicle further comprising the steps of:

-   -   decoupling leg-positioning along the length of the frame,        corresponding to the major axis, from the leg-positioning along        the width of the frame and normal to the major axis and parallel        to the ground;    -   controlling stability of balance over time in the roll direction        primarily, wherein the plurality of leg mechanisms attached to        the frame, one behind the other, along the major axis reduce the        need for pitch control.

According to another aspect of the invention, the method of operatingthe legged vehicle further includes leaning the vehicle into a desireddirection of turn, wherein a projected center of gravity is laterallydisplaced inwardly from a point within a triangle defined by footcontact with the ground, wherein a torque is developed around the rollaxis in the direction of the lean; and displacing one or more feetnormal to and spatially distant from the projected center of gravity inthe opposite direction of the lean to develop an outward torque aboutthe roll axis to counteract the inward lean, wherein the trajectorybecomes a curved line.

According to a further aspect of the invention, the method of operatingthe legged vehicle further includes developing torque from at least oneleg or a combination of two or more legs to rotate the frame along acurved trajectory. This aspect is important for understanding the “leaninto the turn maneuver” and may precede the turn, occur continuously ordiscretely during the turn, and/or provides a means for exiting the turnto pursue a different trajectory.

According to a further aspect of the invention, the method of operatingthe legged vehicle further includes sensing with at least one of agyroscope and accelerometer an induced roll condition from an externalforce; and leaning the vehicle into the direction from which theexternal force is applied, wherein the roll condition is neutralized,according to the control system. Examples of external forces include,but are not limited to wind forces, impulse forces, centripetal forces,and gravitational forces (due to loss of traction causing the frame tofall over). Leaning the vehicle may be accomplished in one of severalways including but not limited to developing a foot-to-ground reactiontorque about the ankle and/or placing one or more feet in the samedirection as the applied external force, beyond the projected center ofgravity plus a distance equal to or greater than is required to counterthe estimated dynamic momentum at the time the foot is repositioned.Furthermore, the external force may be desired, to initiate a lean intoa turn maneuver, for example, but ultimately the roll condition must beneutralized to maintain an upright vehicle posture.

According to a further aspect of the invention, the method of operatingthe legged vehicle further comprises:

-   -   leaning into a turn by balancing the centripetal forces of the        frame, as exemplified through the displacement of the center of        pressure from foot placement with an acceleration force of the        legs. The method of turning the legged vehicle may include the        steps of: leaning the vehicle into a desired direction of turn,        wherein a projected center of gravity is laterally displaced        inwardly from a point within a triangle defined by foot contact        with the ground, wherein a torque is developed around the roll        axis in the direction of the lean; and displacing one or more        feet normal to and spatially distant from the projected center        of gravity in the opposite direction of the lean to develop an        outward torque about the roll axis to counteract the inward        lean, wherein the trajectory becomes a curved line.

The outward and inward torques may be adjusted as necessary to conformto a desired radius of turn. Of course by leaning into the turn, aninward torque, toward the radius of the turn, is created by gravity dueto the unstable positioning of the projected center of pressure. It isnecessary to create a sufficient outward (centripetal) force fromseveral leg movements to balance the inward force. The legs movementsmove the legged vehicle along the desired curved line, or around thedesired radius of turn. The turn may be stopped or changed as desiredthrough leg movements arranged to adjust the position of the projectedcenter of pressure.

This arrangement provides a distinct advantage in that the leggedvehicle may be ridden like a bicycle or motorcycle, and combining thenarrow profile of a two-wheeled vehicle with the sure-footed flexibilityof a legged vehicle.

According to a further aspect of the invention, the control systemincludes a predictive control system, wherein the predictive controlsystem performs the steps of:

-   -   measuring forward body speed, body height, and ground contact        duration for each foot;    -   adjusting the forward body speed, body height, and ground        contact duration for each foot to achieve a set of expected        values according to the desired trajectory;    -   continually determining deviations from the expected values;    -   compensating for the deviations to achieve active balance of the        legged vehicle.

According to a further aspect of the invention, the states of the leggedvehicle include a stance phase, a flight phase, a flight-to-stancephase, and a stance-to-flight phase for each leg. Additional statesregarding the position of the frame, legs and movements andaccelerations of portions of the legged vehicle may also be monitoredvia various sensors described herein. Accurate information regarding thepositions and movement of each component of the legged vehicle permitsaccurate control of the individual components and the successfulguidance of the legged vehicle along a desired trajectory.

According to a further aspect of the invention, the leg mechanisms, suchas the actuators, are controlled by the control system to selectivelyinduce roll, pitch and/or yaw torques between each foot and the ground.

According to a further aspect of the invention, the shape of each footis curved normal to the major axis of travel, and having a radius ofcurvature between an ankle joint and a hip joint, to improve surfacecontact of the foot with the ground while the vehicle is leaning about aroll axis along the major axis of travel. This provides amore-predictable and stable foot-to-ground interface arrangement, whichencourages more positive and predictable movement of the legged vehicleover the ground.

According to a further aspect of the invention, a bottom surface of thefeet include an elastic gripping material to conform to irregularterrain and provide traction.

According to a further aspect of the invention, the body is jointed andincludes two or more segments being joined by a plurality of actuators,position-sensors and elastic components. Such an arrangement providessuperior flexibility and adaptability to a wide range of terrains, andenables the legged vehicle to traverse a wide range of terrains quickly.

According to a further aspect of the invention, each leg mechanismincludes one or more of solid/liquid phase-measurement,temperature-measurement and texture-sensing components providingfeedback to the control system. This knowledge of the various attributesof the environment the legged vehicle is traveling in permits thecontrol system to apply a most appropriate gait for the conditions,which increases safety and efficiency.

According to a further aspect of the invention, at least one leg of thelegged vehicle includes at least three degrees of freedom (DOF).

According to a further aspect of the invention, the three degrees offreedom may be defined by pitch and roll movement at a hip joint and mayinclude extension and retraction of the leg by knee and ankle jointswhich define a spatial volume for possible leg placement.

According to a further aspect of the invention, the movement range foreach of the legs defines a working envelope, each of the feet havingsufficient reach and movement range in length, width and height,relative to the body, to be placed in a plurality of predeterminedlocomotion and dynamic attitude stabilization patterns.

According to a further aspect of the invention, the movement range foreach of the legs defines a working envelope, each of the feet havingsufficient reach and movement range in length, width and height,relative to the body, to be placed in at least one omni-directionallocomotion pattern. Motion along the major axis of the frame, is onlyone of the possible directions of travel. The movement ranges for thelegs, and the actuator/control system interface permit the leggedvehicle to move in any direction along the ground. Motion normal to themajor axis may be in a side-step pattern, which will be described below.

According to a further aspect of the invention, the body includes two ormore segments and is jointed in at least one axis between adjacent legssuch that the feet have sufficient range of movement in length, widthand height to provide overlap of the working envelopes of at least twolegs at any one time. This arrangement provides flexibility to place thelegged vehicle into a stable bipedal or tripedal state wheneverdesirable.

According to a further aspect of the invention, the body is jointed inat least one axis between adjacent legs wherein the body is conformablyflexible to the curvature of a single track turn maneuver. Thisarrangement provides a minimally narrow profile relative to the majoraxis of motion whereby the legged vehicle can engage in propersingle-track operations, such as along a narrow trail or through adoorway.

According to a further aspect of the invention, the body is jointed inat least one axis between adjacent legs wherein the body is conformablyflexible to ground undulations and uneven ground. This arrangementprovides a minimally narrow profile relative to the major axis of motionwherein the legged vehicle can be engaged in proper single-trackactivities, such as walking along a narrow trail and walking through adoorway.

According to a further aspect of the invention, the body includeselastic energy storage and release components between body segments,wherein the elastic components operate in at least one axis, wherein theelastic components store and release kinetic energy for transfer betweenadjacent body segments and adjacent legs. The elastic members may beused to accept and release energy in a predictable manner. This energymay be used by the control system to supplement the leg and/or bodyactuators in placing legs/feet at desired footholds rapidly andaccurately.

According to a further aspect of the invention, the control systemfurther comprises an omni-directional guidance, navigation, and controlalgorithm. The legged vehicle is not confined to motion in a singledirection. The control system may include a number of omni-directionalgaits to facilitate quick and coordinated legged movement in any desireddirection over the ground.

According to a further aspect of the invention, the at least one gaitmodel comprises a clock-driven model of the support phases andswing/flight phases of the gait. This clock-driven model provides abasic amount of timing and coordination for each leg, relative to theother legs, for achieving a coordinated walking motion over the ground.Although a strict time might be inferred, the control system may includethe capability to make minor adjustments to the timing of the phases ofeach leg to adapt to available footholds, or the lack thereof, and thevelocity and trajectory guidance from a user through the control system.

According to a further aspect of the invention, the forward velocity andbody height parameters are predetermined for the at least one gaitmodel. These predetermined parameters remove the requirement for thecontrol system to try to determine unique and optimal velocity and bodyheight (elevation) parameters each time a certain gait is selected.Instead, predetermined parameters of this sort decrease the demands onthe control system.

According to a further aspect of the invention, the forward velocity andbody height parameters are adapted for the at least one gait model usingsensed or a priori ground height map data.

According to a further aspect of the invention, the control systemcomprises at least one of gravity-based sensors,triangulation-measurement devices, echolocators, reference systems,inertial measurement units and digital image processors. Each of thesedevices, alone or in combination, may be used to enhance the control ofthe legged vehicle. Echolocators, reference systems and digital imageprocessors may be used to find and identify possible foothold locations,for example. Each may also be used to find and determine an “up”direction with respect to the frame.

According to a further aspect of the invention, the operator interfaceof the control unit is in wireless communication with the controlsystem. This means that the operator interface does not need to beclosely associated with the legged vehicle. The operator interface maybe remotely located, anywhere within wireless communication range,according to known techniques.

According to a further aspect of the invention, the operator interfaceis attached to the vehicle body. This arrangement is particularly usefulwhere the operator is a rider or passenger aboard the legged vehicle.

According to a further aspect of the invention, the operator interfaceincludes at least one saddle, seat, stirrup, peg, handlebar, and bodyskin. These features may be used to aid in the rider mounting thevehicle, as support while riding the vehicle, or to increase the rider'sability to stay in the saddle and control the vehicle.

According to a further aspect of the invention, the operator interfacecomponents may include at least one position-measuring componentproviding feedback to the control system. The position-measuringcomponent here may be used to measure the position of a rider, operator,cargo or other onboard feature of the legged vehicle. The measurement ofa position of someone/something aboard the legged vehicle may be used bythe control system to adjust the forces applied by the actuators througheach leg.

According to a further aspect of the invention, the operator interfacecomponents include at least one force-measuring component providingfeedback to the control system. These components may be used to measureforces input from a rider/operator or passenger. Various attributes andcontrol functions may be associated with different force components,such as might be used when riding a horse, bicycle or motorcycle. Theforce-measuring components may be placed on a saddle/seat, foot pegs, orother points of contact to measure rider inputs from hands, buttocks,thighs and feet, and to provide control inputs accordingly.

According to a further aspect of the invention, the operator interfacecomponents include at least one torque-measuring component providingfeedback to the control system. Torque-measurement components permitrider/operator-induce torques, such as through handlebars, to berecognized and applied through the control system.

According to a further aspect of the invention, the inputs to theoperator interface control stability of balance in the roll axis. As thelegged vehicle is generally stable in the pitch axis and along the majordirection, the rider inputs may be used to affect roll axis inputs.

According to a further aspect of the invention, the control systemoperates autonomously without operator input. A basic trajectory and/ordestination may be the only requirements for input when the leggedvehicle is underway.

According to a further aspect of the invention, the control system,according to an elastic leg model stored in the read-only-memory,predicts the elastic deformation of the at least one in-line legs in asupport phase (contact) with the ground and/or the elastic deformationof jointed body segments to maintain body stability.

In accordance with a further embodiment of the invention, a method ofoperating a legged vehicle includes the steps of:

-   -   alternating periods of dynamic momentum and periods of tripod        stance;    -   continually sensing body attitude and roll angle with an        inertial measurement unit;    -   during a flight phase for each leg, controlling leg placement        and movement to maintain an upright body position, during both        the flight phase and a stance phase, with the control system,        based upon attitude and roll angle sensor data,    -   during the stance phase for each leg, controlling leg movement,        torque, extension velocity and refraction velocity to meet        desired trajectory requirements.

According to yet a further embodiment of the invention, a method ofoperating a legged vehicle includes the steps of:

-   -   decoupling leg-positioning along the length of the body,        corresponding to the major axis, from the leg-positioning along        the width of the body and normal to the major axis and parallel        to the ground;    -   controlling stability of balance in the roll direction        primarily, wherein the orientation of the leg attachment points        to the body reduce the need for pitch control.

According to a further embodiment of the invention, a method oftraversing a vertical gradient from a lower ground to a higher groundwith a legged vehicle includes the steps of:

-   -   establishing a stance phase with the center of pressure of the        body inside a triangle defined by three feet, which defines a        triangular support pattern, including a front foot, a middle        foot and a rear foot attached to separate legs which are        attached to a forward, middle and rear of the body,        respectively;    -   lowering a portion of the body that is farthest from the        vertical gradient, corresponding to a rear portion, and shifting        the center of pressure rearward to approach a zero-moment line        bisecting the centers of the middle and rear feet;    -   lifting the body on the middle and rear legs while        simultaneously lifting the front foot from the lower ground;    -   repositioning the front foot beyond the vertical gradient to a        position above the upper ground;    -   extending the middle foot, corresponding to the front-most foot        of the middle and rear feet, to a position approaching its        maximum extension;    -   moving the front foot forward while maintaining the center of        pressure near the zero-moment line bisecting the center of the        middle foot and rear foot;    -   placing the front foot on the upper ground,    -   re-establishing the triangular support pattern; and    -   counteracting any dynamic instability with the triangular        support pattern.

According to a further embodiment of the invention, a method oftraversing a vertical gradient from a lower ground to a higher groundwith a legged vehicle includes the steps of:

-   -   shifting the center of pressure to a zero-moment line bisecting        the center of the front foot and the rear foot;    -   lifting the middle foot and repositioning the middle foot above        the upper ground;    -   placing the middle foot on the upper ground;    -   re-establishing the triangular support pattern; and    -   counteracting any dynamic instability with the triangular        support pattern.

According to a further embodiment of the invention, a method oftraversing a vertical gradient from a lower ground to a higher groundwith a legged vehicle includes the steps of:

-   -   shifting the center of pressure to the zero-moment line        bisecting the center of the front foot and the middle foot;    -   lifting the rear foot and repositioning the rear foot above the        upper ground;    -   placing the rear foot on the upper ground;    -   re-establishing the triangular support pattern; and    -   counteracting any dynamic instability with the triangular        support pattern.

According to a further embodiment of the invention, a method oftraversing a vertical gradient from a lower ground to a higher groundwith a legged vehicle includes the steps of:

-   -   lifting the body;    -   shifting the center of pressure to the zero-moment line that        bisects the centers of the front foot and the rear foot;    -   repositioning the middle foot to a position forward and beyond        the front foot;    -   re-establishing the triangular support pattern; and    -   counteracting any dynamic instability with the triangular        support pattern.

According to a further embodiment of the invention, a method oftraversing a vertical gradient from a lower ground to a higher groundwith a legged vehicle includes the steps of:

-   -   shifting the center of pressure to the zero-moment line that        bisects the centers of the middle foot and the rear foot;    -   repositioning the front foot to the forward-most position while        simultaneously moving the body forward; and    -   maintaining forward motion by one of a plurality of        predetermined gaits.

According to another embodiment of the invention, a method of performinga gait with a legged vehicle includes the steps of:

-   -   determining a plurality of candidate footfall positions with a        sensor in communication with the control system;    -   selecting one or more footfall positions, including a most        desirable footfall position based on a number of factors;    -   selecting a target walking pattern model from a plurality of        walking pattern models stored in ROM of the control system,        wherein each target walking pattern includes a clock-driven        model of the support and flight phases of the gait for each leg,        wherein the selection is based upon a number of factors,        including the desired velocity and the terrain;    -   computing a desired trajectory for the body of the vehicle, such        as with heuristic and simulation algorithms;    -   selecting a pattern of footholds from a set of reachable        footholds that most closely correspond to the desired        trajectory, and which minimize dynamic momentum for lateral and        roll axes;    -   utilizing dynamic momentum to maintain the desired body        trajectory during periods of single-leg support and double-leg        support;    -   performing at least one of repeating the walking pattern model        as desired and selecting a different walking pattern model until        a desired destination is achieved.

According to a further embodiment of the invention, a method ofperforming a wave gait with a legged vehicle according to a clock-drivenmodel of the support and flight phases of the gait for each leg,including the steps of:

-   -   determining a master time period, including overlapping and        simultaneous first, second and third time periods corresponding        to first, second and third legs and feet, respectively,    -   driving a front foot and leg rearward with respect to the body        while in a first stance phase, wherein the foot is generally        stationary with respect to the ground, wherein the body moves in        a forward direction according to the major axis during a first        time period;    -   lifting the front foot and leg and swinging the front foot and        leg forward during a first flight phase;    -   lowering the front foot and leg to the ground to end the first        flight phase;    -   repeating the first stance and first flight phases;    -   driving a middle foot and leg rearward with respect to the body        while in a second stance phase, wherein the body moves in a        forward direction according to the major axis during a second        time period;    -   lifting the middle foot and leg and swinging the middle foot and        leg forward during a second flight phase;    -   lowering the middle foot and leg to the ground to end the second        flight phase;    -   repeating the second stance and second flight phases;    -   driving a rear foot and leg rearward with respect to the body        while in a third stance phase, wherein the body moves in a        forward direction according to the major axis during a third        time period;    -   lifting the rear foot and leg and swinging the rear foot and leg        forward during a third flight phase;    -   lowering the rear foot and leg to the ground to end the third        flight phase;    -   repeating the third stance and third flight phases.

According to a further aspect of the invention, the method of performinga wave gait with a legged vehicle further includes:

-   -   separating the first, second and third flight phases to        eliminate overlap, wherein at least two feet are on the ground        at any time.

According to a further aspect of the invention, the method of performinga wave gait with a legged vehicle further includes:

-   -   dividing the master time period and each of the first, second        and third time periods into a plurality of equal sub-units,        wherein the sub-units define when the first, second and third        feet and legs are in the stance and flight phases.

According to a further aspect of the invention, the method of performinga wave gait with a legged vehicle further includes:

-   -   evenly spacing the flight phases for the first, second and third        feet and legs, wherein at least two feet are on the ground        during each sub-unit.

According to a further aspect of the invention, the method of performinga wave gait with a legged vehicle further includes:

-   -   providing at least ten sub-units in the master time period and        each of the first, second and third time periods;    -   performing a flight phase for each leg and foot during at least        one sub-unit, wherein the at least one sub-unit for each leg and        foot are during different parts of the master time period and do        not overlap;    -   performing a stance phase for each leg and foot when not in a        flight phase.

According to a further aspect of the invention, the method of performinga wave gait with a legged vehicle further includes:

-   -   dividing the master time period and each of the first, second        and third time periods into eleven equal sub-units, wherein the        sub-units define when the first, second and third feet and legs        are in the stance and flight phases,    -   performing the flight phase for the first leg and foot at time        period eleven, a single subunit;    -   performing the flight phase for the second leg and foot at time        period six, a single subunit;    -   performing the flight phase for the third leg and foot at time        period one, a single subunit, wherein each stance phase for each        leg is ten sub-units in duration.

According to a further aspect of the invention, the method of performinga wave gait with a legged vehicle further includes:

-   -   dividing the master time period and each of the first, second        and third time periods into twelve equal sub-units, wherein the        sub-units define when the first, second and third feet and legs        are in the stance and flight phases,    -   performing the flight phase for the first leg and foot at time        periods eleven and twelve, which is two sub-units;    -   performing the flight phase for the second leg and foot at time        periods six and seven, which is two sub-units;    -   performing the flight phase for the third leg and foot at time        periods one and two, which is two sub-units, wherein each stance        phase for each leg is ten sub-units in duration.

According to a further aspect of the invention, the method of performinga wave gait with a legged vehicle further includes:

-   -   dividing the master time period and each of the first, second        and third time periods into twelve equal sub-units, wherein the        sub-units define when the first, second and third feet and legs        are in the stance and flight phases,    -   performing the flight phase for the first leg and foot at time        periods nine through twelve, which is four sub-units;    -   performing the flight phase for the second leg and foot at time        periods five through eight, which is four sub-units;    -   performing the flight phase for the third leg and foot at time        periods one through four, which is four sub-units, wherein each        stance phase for each leg is eight sub-units in duration.

According to a further aspect of the invention, the method of performinga wave gait with a legged vehicle further includes:

-   -   performing one of a make before break transition and a break        before make transition when two legs are scheduled to end a        flight phase and begin a flight phase, respectively, at the same        time,    -   wherein the make before break transition includes the flight        phase for one leg ending before the flight phase begins for        another leg, and wherein the break before make transition        includes the flight phase for one leg beginning before the        flight phase has ended for another leg.

According to a further aspect of the invention, the method of performinga wave gait with a legged vehicle further includes:

-   -   performing the flight phases immediately consecutively for the        first, second and third feet and legs, wherein at least two feet        are on the ground during each sub-unit.

According to a further aspect of the invention, the method of performinga wave gait with a legged vehicle further includes:

-   -   dividing the master time period and each of the first, second        and third time periods into twelve equal sub-units, wherein the        sub-units define when the first, second and third feet and legs        are in the stance and flight phases,    -   performing the flight phase for the first leg and foot at time        periods eleven and twelve, which is two sub-units;    -   performing the flight phase for the second leg and foot at time        periods nine and ten, which is two sub-units;    -   performing the flight phase for the third leg and foot at time        periods seven and eight, which is two sub-units, wherein each        stance phase for each leg is ten sub-units in duration.

According to a further aspect of the invention, the method of performinga wave gait corresponding to a trot gait with a legged vehicle furtherincludes:

-   -   dividing the master time period and each of the first, second        and third time periods into eleven equal sub-units, wherein the        sub-units define when the first, second and third feet and legs        are in the stance and flight phases,    -   performing the flight phase for the first leg and foot at time        periods nine through eleven, which is three sub-units;    -   performing the flight phase for the second leg and foot at time        periods five through seven, which is three sub-units;    -   performing the flight phase for the third leg and foot at time        periods one through three, which is three sub-units;    -   supporting the body with three legs twice during the master time        period, wherein each stance phase for each leg is eight        sub-units in duration.

According to a further aspect of the invention, the method of performinga wave gait with a legged vehicle further includes:

-   -   separating the first, second and third stance phases so that at        least one, but no more than two feet are on the ground at any        time.

According to a further aspect of the invention, the method of performinga wave gait corresponding to an equal phase backward wave gait with alegged vehicle further includes:

-   -   dividing the master time period and each of the first, second        and third time periods into twelve equal sub-units, wherein the        sub-units define when the first, second and third feet and legs        are in the stance and flight phases,    -   performing the flight phase for the first leg and foot at time        periods seven through twelve, which is six sub-units;    -   performing the flight phase for the second leg and foot at time        periods four through nine, which is six sub-units;    -   performing the flight phase for the third leg and foot at time        periods one through six, which is six sub-units;    -   supporting the body with only one leg twice during the master        time period, wherein each stance phase for each leg is six        sub-units in duration, wherein the stance phases for each leg        are equal and the flight phases for each leg are of equal        duration;    -   performing body attitude and roll corrections during the stance        phases for each of the legs based upon body attitude and roll        sensory data to the control system.

According to a further aspect of the invention, the method of performinga wave gait corresponding to an equal phase backward wave gait with alegged vehicle further includes:

-   -   dividing the master time period and each of the first, second        and third time periods into six equal sub-units, wherein the        sub-units define when the first, second and third feet and legs        are in the stance and flight phases,    -   performing the flight phase for the first leg and foot at time        periods six through one, which is two sub-units;    -   performing the flight phase for the second leg and foot at time        periods two through four, which is two sub-units;    -   performing the flight phase for the third leg and foot at time        periods six through one, which is two sub-units;    -   supporting the body with only one leg once during the master        time period;    -   supporting the body with three legs twice during the master time        period, wherein each stance phase for each leg is four sub-units        in duration, wherein the stance phases for each leg are equal        and the flight phases for each leg are of equal duration;    -   performing body attitude and roll corrections during the stance        phases for each of the legs based upon body attitude and roll        sensory data to the control system.

According to a further aspect of the invention, the method of performinga wave gait corresponding to an equal phase backward wave gait fortrotting or pacing with a legged vehicle further includes:

-   -   dividing the master time period and each of the first, second        and third time periods into twelve equal sub-units, wherein the        sub-units define when the first, second and third feet and legs        are in the stance and flight phases,    -   performing the flight phase for the first leg and foot at time        periods one through six, which is six sub-units;    -   performing the flight phase for the second leg and foot at time        periods seven through twelve, which is six sub-units;    -   performing the flight phase for the third leg and foot at time        periods one through six, which is six sub-units;    -   supporting the body with only one leg once during the master        time period;    -   supporting the body with two legs once during the master time        period, wherein each stance phase for each leg is six sub-units        in duration, wherein the stance phases for each leg are of equal        duration and the flight phases for each leg are of equal        duration;    -   performing body attitude and roll corrections when the first and        third legs are in the stance phase, based upon body attitude and        roll sensory data to the control system;    -   utilizing dynamic momentum of the body to maintain body attitude        when only the second leg is in the stance phase.

According to a further aspect of the invention, the method of performinga wave gait corresponding to a backward wave gait with a legged vehiclefurther includes:

-   -   dividing the master time period and each of the first, second        and third time periods into twelve equal sub-units, wherein the        sub-units define when the first, second and third feet and legs        are in the stance and flight phases,    -   performing the flight phase for the first leg and foot at time        periods one through eight, which is eight sub-units;    -   performing a first flight phase for the second leg and foot at        time periods two through five, which is four sub-units;    -   performing a second flight phase for the second leg and foot at        time periods eight through eleven, which is four sub-units;    -   performing the flight phase for the third leg and foot at time        periods five through twelve, which is eight sub-units;    -   supporting the body with only one leg twice during the master        time period;    -   supporting the body with three legs, a stance phase, twice        during the master time period;    -   performing body attitude and roll corrections during the stance        phases for each of the legs based upon body attitude and roll        sensory data to the control system.

According to a further aspect of the invention, the method of performinga wave gait corresponding to a backward wave gait with a legged vehiclefurther includes:

-   -   performing at least one of a make before break maneuver and a        break before make maneuver.

According to a further aspect of the invention, the method of performinga wave gait corresponding to a backward wave gait with a legged vehiclefurther includes:

-   -   repositioning the second leg and foot during the master time        period.

According to a further aspect of the invention, the method of performinga wave gait corresponding to a forward and backward wave gait with alegged vehicle further includes:

-   -   dividing the master time period and each of the first, second        and third time periods into twelve equal sub-units, wherein the        sub-units define when the first, second and third feet and legs        are in the stance and flight phases,    -   performing the flight phase for the first leg and foot at time        periods three through ten, which is eight sub-units;    -   performing a first flight phase for the second leg and foot at        time periods five through eight, which is four sub-units;    -   performing a second flight phase for the second leg and foot at        time periods eleven through two, which is four sub-units;    -   performing the flight phase for the third leg and foot at time        periods nine through four, which is eight sub-units;    -   performing body attitude and roll corrections based upon body        attitude and roll sensory data to the control system.

According to a further aspect of the invention, the method of performinga wave gait corresponding to a forward and backward wave gait with alegged vehicle further includes:

-   -   performing at least one of a make before break maneuver and a        break before make maneuver.

According to a further aspect of the invention, the method of performinga wave gait corresponding to a forward and backward wave gait with alegged vehicle further includes:

-   -   repositioning the second leg and foot during the master time        period.

According to a further aspect of the invention, the method of performinga wave gait corresponding to a fast trot and hopping gaits with a leggedvehicle further includes:

-   -   dividing the master time period and each of the first, second        and third time periods into an equal number of sub-units,        wherein the sub-units define when the first, second and third        feet and legs are in the stance and flight phases,    -   providing hopping force during a stance phase with the second        leg for a single sub-unit;    -   providing pitch stability of the body during a stance phase with        the first leg and third leg for a single sub-unit,    -   performing a flight phase for all legs simultaneously for at        least a single sub-unit, wherein the legged vehicle is in a        ballistic flight phase;    -   performing body attitude and roll corrections based upon body        attitude and roll sensory data to the control system, wherein        the stance phase for the second leg and the stance phase for the        first and third legs are separated by at least one sub-unit.

According to a further aspect of the invention, the method of performinga wave gait corresponding to a running model gait with a legged vehiclefurther includes:

-   -   dividing the master time period and each of the first, second        and third time periods into an equal number of sub-units,        wherein the sub-units define when the first, second and third        feet and legs are in the stance and flight phases,    -   providing the stance phase for the first leg for a single        sub-unit;    -   providing the stance phase for the second leg for a single        sub-unit, wherein the stance phase for the first leg and the        stance phase for the second leg are separated by at least a        sub-unit;    -   providing the stance phase for the third leg for a single        sub-unit, wherein the stance phase for the second leg and the        stance phase for the third leg are separated by at least a        sub-unit, and wherein the stance phase for the third leg and the        stance phase for the first leg are separated by at least a        sub-unit;    -   providing pitch stability of the body during the stance phases        with the first leg, second leg and third leg separately for a        single sub-unit;    -   performing a flight phase for all legs simultaneously for at        least a single sub-unit, wherein the legged vehicle is in a        ballistic flight phase;    -   performing body attitude and roll corrections based upon body        attitude and roll sensory data to the control system.

According to a further aspect of the invention, the method of performinga gait corresponding to a pronking model gait with a legged vehiclefurther includes:

-   -   dividing the master time period and each of the first, second        and third time periods into an equal number of sub-units,        wherein the sub-units define when the first, second and third        feet and legs are in the stance and flight phases,    -   providing the stance phase for the first leg, second leg and        third leg simultaneously for a single sub-unit;    -   separating consecutive stance phases by a flight phase of at        least one sub-unit;    -   providing pitch stability of the body during the stance phases        with the first leg, second leg and third leg separately during        the at least one single sub-unit;    -   performing the flight phase for all legs simultaneously for at        least a single sub-unit, wherein the legged vehicle is in a        ballistic flight phase;    -   performing body attitude and roll corrections based upon body        attitude and roll sensor data to the control system.

According to a further aspect of the invention, the method of performinga gait corresponding to a bounding model gait with a legged vehiclefurther includes:

-   -   dividing the master time period and each of the first, second        and third time periods into an equal number of sub-units,        wherein the sub-units define when the first, second and third        feet and legs are in the stance and flight phases,    -   providing the stance phase for the first leg for time periods        one through three, which is three sub-units;    -   providing the stance phase for the second leg for time periods        two through four, which is three sub-units;    -   providing the stance phase for the third leg for time periods        three through five, which is three sub-units, and wherein the        stance phases for the first leg, second leg and third leg        overlap by at least one sub-unit;    -   providing a flight phase for three sub-units for each leg        immediately following the stance phase for each leg;    -   providing pitch stability of the body during the stance phases        with the first leg, second leg and third leg;    -   performing a flight phase for all legs simultaneously for at        least one single sub-unit, wherein the legged vehicle is in a        ballistic flight phase;    -   performing body attitude and roll corrections based upon body        attitude and roll sensory data to the control system.

According to a further aspect of the invention, the method of operatinga legged vehicle further includes the steps of:

-   -   operating the legged vehicle in at least one of a fully        autonomous mode requiring no input to achieve its destination        once programmed, a partially-autonomous mode with remote control        inputs, and a partially-autonomous mode with rider-operator        control inputs,    -   wherein for the fully autonomous mode, providing into the        control system a desired destination and one or more of a        desired route and a desired velocity,    -   wherein for the partially-autonomous mode with remote inputs,        providing temporal inputs into the control system by a remote        operator interface,    -   wherein for the partially-autonomous mode with rider-operator        control inputs, providing temporal inputs into the control        system by a rider-operator of the legged vehicle.

According to another embodiment of the invention, the method ofoperating a legged vehicle, wherein the fully autonomous control and thepartially-autonomous control includes the steps of

-   -   sensing terrain with a sensor in communication with the control        system;    -   planning a path based on control inputs and sensed terrain        inputs;    -   selecting footholds for each foot according to the walking gait        model selected, the path planned, and the sensed terrain.

According to a further aspect of the invention, the method of operatinga legged vehicle, wherein the fully autonomous control and thepartially-autonomous control further includes the step of:

-   -   adjusting forward- and side-step length according to the        foothold selections.

According to a further aspect of the invention, the method of operatinga legged vehicle, wherein the fully autonomous control and thepartially-autonomous control further includes the step of:

-   -   actively maintaining stabilization and balance of the body.

According to another embodiment of the invention, the method ofoperating a legged vehicle with a predictive control system, includingthe steps of:

-   -   measuring forward body speed, body height, and ground contact        duration for each foot;    -   adjusting the forward body speed, body height, and ground        contact duration for each foot to achieve a set of expected        values according to the desired trajectory;    -   continually determining deviations from the expected values;    -   compensating for the deviations to achieve active balance of the        legged vehicle.

According to a further aspect of the invention, the method of operatinga legged vehicle with a predictive control system, wherein thedeviations are due to at least one of mechanical losses, weather andwind, rider-operator-induced perturbations, and variable groundconditions.

According to a further aspect of the invention, the legged vehicleincludes three legs attached to the frame in an in-line fashion, whereinthe second or middle leg is capable of supporting the entire weight ofthe vehicle, rider and any cargo and the first (front) and third (rear)legs are capable of at least partially supporting the entire weight ofthe vehicle, rider, and cargo.

According to another aspect of the invention, the method of executingstraight-line walking with an in-line legged vehicle utilizes afour-phase cycle for each leg, the four phases including:

-   -   a stance or support phase wherein foot-to-ground interaction is        developed to produce reaction forces and torques that are        transferred from the foot through the leg to stabilize the body        in the pitch, roll, and yaw axes and to propel the body in the        x, y, and z axes, the stance foot being generally stationary        with respect to the ground and moving generally opposite in        direction to the major direction of body motion,    -   a stance-to-flight phase wherein the reaction forces between the        foot and the ground are unloaded and the foot is lifted off the        ground,    -   a flight phase wherein the leg is moved to reposition its foot        by moving the foot in the same general direction and generally        at a faster (negative) rate as the major direction of body        motion, and    -   a flight-to-stance phase wherein the foot is placed on the        ground and reaction forces and torques are developed between the        foot and the ground.

According to a further aspect of the invention, the method of executingstraight-line walking with an in-line legged vehicle is according to awave gait.

According to another aspect of the invention, the method of executingstraight-line walking with an in-line legged vehicle includes the stepsof:

-   -   tracking and synchronizing each phase for each leg, according to        a selected predetermined gait model, with a state machine.

According to another aspect of the in-line legged vehicle for executingstraight-line walking further includes

-   -   wherein the control system modifies the duration of each phase        of the four phases of walking motion for a plurality of legs        executing a pre-defined gait according to a preprogrammed        strategy to perform useful work, such as speeding up, slowing        down, or stepping on a forbidden region.

According to another aspect of the invention, the method of executingstraight-line walking with an in-line legged vehicle,

-   -   wherein the combined ground reaction forces between at least two        feet during stance phase imparts a force which propels the body        in the x, y, and z axes and a torque which rotates the body in        the pitch, roll, and/or yaw axes.

According to another aspect of the invention, the method of executingstraight-line walking with an in-line legged vehicle,

-   -   wherein the length of each leg is varied with respect to the        body height during a stance phase such that the body is stable        in height and pitch over uneven ground, within the working range        of the legs and their feet.

According to another aspect of the invention, the method of executingstraight-line walking with an in-line legged vehicle,

-   -   wherein the body/frame is inclined/reclined in the pitch axis to        lower/raise the front of the body and to raise/lower the rear of        the body when ascending/descending a gradient, within the        working range of the legs and their feet.

According to another aspect of the invention, the method of executingstraight-line walking with an in-line legged vehicle,

-   -   wherein the body height normal to the ground is lowered when        ascending or descending a gradient, within the working range of        the legs and their feet.

According to another aspect of the invention, the method of executingstraight-line walking with an in-line legged vehicle,

-   -   wherein a foot is positioned to the right or to the left of the        projected center of gravity on to the ground to develop during a        stance phase:        -   1) additional ground reaction forces that are normal to the            major direction of motion and        -   2) ground reaction torques in the pitch, roll, and/or yaw            axes.

According to another aspect of the invention, the method of executingstraight-line walking with an in-line legged vehicle,

-   -   wherein the leg length during a stance phase is different        between feet positioned to the right or to the left of the        projected center of gravity of the body on to the ground in        order to level the body attitude, within the working range of        the legs and their feet.

According to another aspect of the invention, the method of executingstraight-line walking with an in-line legged vehicle,

-   -   wherein the body height normal to the ground is lowered when        walking along a gradient, within the working range of the legs        and their feet.

According to another aspect of the invention, the method of executingstraight-line walking with an in-line legged vehicle,

-   -   wherein retraction of the legs during flight phase is inwards        towards the body and along the major direction of motion such        that no torque is imparted to the body in the roll axis.

According to another aspect of the invention, the method of executingstraight-line walking with an in-line legged vehicle,

-   -   wherein the leg is swept/swung outward during a flight phase        without reducing its length to impart a torque in the pitch,        roll and/or yaw axes to aid in stabilizing the body.

According to another aspect of the invention, the method of executingstraight-line walking with an in-line legged vehicle, further comprisingthe steps:

-   -   sweeping/swinging a leg outward from the body and away from the        ground;    -   reducing the length of the leg, such as by bending the leg at        the knee;    -   sweeping the shortened leg back inward towards the ground during        a flight phase to impart a torque in the pitch, roll and/or yaw        axes to aid in stabilizing the body.

According to another aspect of the invention, the method of executingstraight-line walking with an in-line legged vehicle,

-   -   wherein two legs transition from stance-to-flight and        flight-to-stance phase in a make before break fashion such that        both feet support the body, and the landing foot is placed        spatially apart from the foot lifting off.

According to another aspect of the invention, the method of executingstraight-line walking with an in-line legged vehicle, wherein a controlsystem positions the landing foot ahead, behind, to the right of or tothe left of the foot lifting off according to a pre-programmed strategy,called a dexterous periodic gait.

According to another aspect of the invention, the method of executingstraight-line walking with an in-line legged vehicle, wherein two feetare positioned one to the left and one to the right of the projectedcenter of gravity of the body onto the ground in a generally bipedalstance with respect to the length of the body and major direction ofmotion to provide a period of stability in the roll axis.

According to another aspect of the invention, the method of executingstraight-line walking with an in-line legged vehicle, wherein thecombined ground reaction forces between two feet during stance phaseimparts a torque to rotate the body in the pitch, roll, and/or yaw axes.

According to another aspect of the invention, the method of executingstraight-line walking with an in-line legged vehicle, wherein three feetare positioned in a tripod stance to provide a period of stability inthe x, y, and z axes and pitch, roll, and yaw axes.

According to another aspect of the invention, the method of executingstraight-line walking with an in-line legged vehicle, wherein thecombined ground reaction forces of said three feet positioned in atripod stance impart a torque in the pitch, roll and/or yaw axes to aidin stabilizing the body.

According to another aspect of the invention, the method of executingstraight-line walking with an in-line legged vehicle, wherein two legstransition from stance to flight and flight to stance in a break beforemake fashion and the landing foot is placed in or near the same footholdas the foot lifting off.

According to another aspect of the invention, the method of executingstraight-line walking with an in-line legged vehicle, wherein the secondfoot is placed in or near the same foothold as the first foot, the thirdfoot is placed in or near the same foothold as the second foot, and soon according to a pre-programmed strategy, called a continuousfollow-the-leader gait.

According to another aspect of the invention, the method of executingstraight-line walking with an in-line legged vehicle, wherein a controlsystem positions the first foot.

According to a further embodiment of the invention, a method ofexecuting a single-track walking turn with an in-line legged vehicle,wherein a yaw torque about the center of gravity is developed by theinteraction of two legs with the ground, according to control systemcontrol of leg actuators.

According to a further embodiment of the invention, a method ofexecuting a single-track walking turn with an in-line legged vehicle,wherein a yaw torque about the center of gravity is developed by theinteraction of one foot with the ground.

According to a further embodiment of the invention, a method of runningwith an in-line legged vehicle, wherein during foot touchdown, the footaccelerates backward with respect to the hip until there is no speeddifferential between the foot and the ground before contact with theground, called ground speed matching.

According to a further embodiment of the invention, a method of runningwith an in-line legged vehicle, wherein during foot lift-off, the footcontinues moving backward until it is fully unloaded.

According to another embodiment of the invention, a method of executinga single-track running turn of an in-line legged vehicle, wherein a foottorque develops a yaw torque about the center of gravity.

According to another embodiment of the invention, a method of executinga single-track running turn of an in-line legged vehicle, wherein anoff-axis force impulse develops a yaw torque about the center ofgravity.

According to a further embodiment of the invention, a method of hoppingof an in-line legged vehicle, wherein a state machine uses sensory datato track the hopping motion to switching leg states on the occurrence ofkey events stored in memory.

According to a further aspect of the invention, the method of hopping ofan inline legged vehicle, wherein the hopping states includecompression, thrust, unloading, flight, and landing.

According to a further aspect of the invention, the method of hopping ofan inline legged vehicle, wherein hopping involves alternatingfoot-patterns of the bipedal and tripedal stance to achieve stability ofbalance.

According to a further embodiment of the invention, a method ofpacing/bounding of an in-line legged vehicle, wherein two legs form apair of legs that work in unison as though they were one leg, strikingthe ground in unison and leaving the ground in unison.

According to a further aspect of the invention, the method ofpacing/bounding of an in-line legged vehicle, wherein diagonal legs formpairs in the trot in a simulated bipedal-like stance.

According to a further aspect of the invention, the method ofpacing/bounding of an in-line legged vehicle, wherein lateral legs formpairs in the pace for a simulated bipedal-like stance.

According to a further aspect of the invention, the method ofpacing/bounding of an in-line legged vehicle, wherein front and rearlegs form a pair in the bound—the middle alternating between front andrear, as required.

According to a further embodiment of the invention, a method of leapingof an in-line legged vehicle, wherein the legs leap from a tripedalstance.

According to a further aspect of the invention, the method of leaping ofan in-line legged vehicle, wherein the legs land in a tripedal stance.

According to a further aspect of the invention, the method of leaping ofan in-line legged vehicle, wherein the legs leap with two legs inbipedal-like stance for balance stability and control.

According to a further aspect of the invention, the method of leaping ofan in-line legged vehicle, wherein the legs land with two legs inbipedal-like stance for balance stability and control.

According to a further embodiment of the invention, a method of jumpingof an in-line legged vehicle, wherein take-off uses two legs inbipedal-like stance for balance stability and control.

According to a further embodiment of the invention, a method of jumpingof an in-line legged vehicle, wherein landing uses two legs inbipedal-like stance for balance stability and control.

According to a further embodiment of the invention, a method of passiverider-based control of an in-line legged vehicle, wherein the legsfollow an in-line path.

According to a further aspect of the invention, the method of passiverider-based control of an in-line legged vehicle, wherein elasticdeformation of the legs aids in compliance with irregular ground height.

According to a further aspect of the invention, the method of passiverider-based control of an in-line legged vehicle, wherein the actuationforce applied by the middle leg is greater than the outer legs.

According to a further aspect of the invention, the method of passiverider-based control of an in-line legged vehicle, wherein handle barsprovide steering angle input.

According to a further aspect of the invention, the method of passiverider-based control of an in-line legged vehicle, wherein the forwardleg initiates the turn with the last leg following.

According to a further aspect of the invention, the method of passiverider-based control of an in-line legged vehicle, wherein the legsfollow a turn based on the commanded steering angle.

According to a further embodiment of the invention, a method ofsemi-autonomous and rider-based control of an in-line legged vehicle,

-   -   wherein the sensors sense an approximately narrow, in-line area.

According to a further aspect of the invention, the method ofsemi-autonomous and rider-based control of an in-line legged vehicle,wherein the control system executes temporal prediction of N stepsahead.

According to a further embodiment of the invention, a method ofautonomously controlling an in-line legged vehicle, wherein the sensorssense an approximately narrow, in-line area.

According to a further aspect of the invention, the method ofautonomously controlling an in-line legged vehicle, wherein the controlsystem executes temporal prediction of N steps ahead.

According to a further embodiment of the invention, a method ofresponding to a de-stabilizing external force of an in-line leggedvehicle,

-   -   wherein transition out of a current gait to new gait is selected        based on minimizing the least mean square error cost to        pre-defined gait patterns stored in memory.

According to a further aspect of the invention, the method of respondingto a de-stabilizing external force of an in-line legged vehicle,

-   -   wherein transition out of a current gait to new gait is selected        based on minimizing the least mean square error cost to        pre-defined gait patterns stored in memory simulated by temporal        prediction of N steps ahead.

According to a further embodiment of the invention, a method of recoveryfrom an out of control situations of an in-line legged vehicle, whereina foot is retracted and thrust in the direction of the roll to catch thebody.

OBJECTS, FEATURES AND ADVANTAGES

It has long been known that it would be advantageous to develop avehicle that uses legs rather than one with wheels because a vehiclewith legs can go where wheeled or treaded vehicles cannot go. Leggedvehicles have improved mobility over rugged terrain with unstablefootholds, such as mountain slopes and piles of rubble, because thelegged vehicles may choose optimal foot placement and vary the length ofthe leg with respect to the body. Additionally, legged vehicles canbound, leap, or jump over areas of ground that do not have a continuouspath of support or closely spaced footholds. Moreover, legged vehiclesare able to move in man-made or cultural environments, traversingobstacles such as curbs, stairs, and narrow passageways. With respect towheeled vehicles, legged vehicles reduce body motion. Thischaracteristic is especially well suited to the comfort of a rider orpassenger.

It is therefore an object of the present invention to solve the problemsassociated with providing a single track or in-line multi-legged mobilerobot similar in form or function to the motorcycle or bicycle but withthe added benefit of legs and full or partial robotic control. Forexample, unlike the wheeled motorcycle or bicycle, a feature andadvantage of the single track or in-line multi-legged mobile robot isthat it can move sideways. It is a feature of this invention to solvethese problems by providing a walking machine in which the legs arein-line or co-linear with respect to the body and primary direction ofmotion. Unlike the wheeled motorcycle or bicycle, the single track orin-line multi-legged mobile robot uses discrete footholds over theduration of the stance period, which is an advantage or feature inrugged, natural terrain where footholds are unevenly spaced. Anotherobject of this invention is to provide a robotic control system, e.g.,autonomous attitude stabilization control, for the single track orin-line multi-legged system. For example in the case where all threelegs are in contact with the ground, as in the stance phase of a wavegait, the ability to shift one of the legs laterally to affect balanceis an advantage or feature. Further, unlike the outrigger wheels of theprior art, the feet of the single track or in-line multi-legged mobilerobot are stationary with respect to footholds during the supportperiod, thus eliminating the drawback of the prior art when used inrugged terrain.

Still other objects, features and attendant advantages of the presentinvention will become apparent to those skilled in the art from readingof the following detailed description of the preferred embodimentconstructed in accordance therewith and taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates a perspective skeletal view of a single track,in-line three legged mobile robot having pantograph legs;

FIG. 2 illustrates a perspective skeletal view of a single track orin-line three legged mobile robot;

FIG. 3 illustrates a perspective skeletal view of a single track,in-line three-legged mobile robot/vehicle having a jointed, articulatedbody/frame;

FIG. 4 illustrates a side skeletal view of a single track or in-linethree legged mobile robot illustrating the range of motion of the legsalong the major direction of travel;

FIG. 5 illustrates a perspective skeletal view of a single track orin-line three legged mobile robot illustrating one possibleconfiguration of the legs, typically used in a stationary stance;

FIG. 6 illustrates a top schematic view illustrating center of gravity,placement of the feet, and resulting area of support for the singletrack or in-line three legged mobile robot illustrated in FIG. 5;

FIG. 7 illustrates a side skeletal view of a single track or in-linethree legged mobile robot illustrating overlap and crossover of thefirst and second legs, typically used while moving;

FIG. 8 illustrates a top schematic view illustrating center of gravity,placement of the feet, and resulting area of support for the singletrack or in-line three legged mobile robot illustrated in FIG. 7;

FIG. 9 illustrates one possible configuration of leg and foot placementbefore traversing a vertical or step gradient for a single track orin-line three legged mobile robot;

FIG. 10 illustrates a top schematic view illustrating center of gravity,placement of the feet, and resulting area of support for the singletrack or in-line three legged mobile robot illustrated in FIG. 9;

FIG. 11 illustrates a single track or in-line legged mobile robotadjusting the walking height and/or body attitude in preparation totraverse a vertical or step gradient;

FIG. 12 illustrates a top schematic view illustrating center of gravity,placement of the feet, and resulting area of support for the singletrack or in-line three legged mobile robot illustrated in FIG. 11;

FIG. 13 illustrates a single track or in-line legged mobile robotlifting itself on the middle and rear legs while simultaneously liftingthe front foot off the ground and repositioning it beyond a vertical orstep gradient;

FIG. 14 illustrates a top schematic view illustrating center of gravity,placement of the feet, and resulting area of support for the singletrack or in-line three legged mobile robot illustrated in FIG. 13;

FIG. 15 illustrates a single track or in-line legged mobile robotshifting its body and thus its projected center of pressure on themiddle and rear legs to move the body and thus the front foot forward,while maintaining balance in a biped stance;

FIG. 16 illustrates a top schematic view illustrating center of gravity,placement of the feet, and resulting area of support for the singletrack or in-line three legged mobile robot illustrated in FIG. 15;

FIG. 17 illustrates, and in particular the upper right insert, shows asingle track or in-line legged mobile robot placing the front foot onthe upper ground and reestablishing the triangular three-point contactsupport pattern;

FIG. 18 illustrates a top schematic view illustrating center of gravity,placement of the feet, and resulting area of support for the singletrack or in-line three legged mobile robot illustrated in FIG. 17;

FIG. 19 illustrates a single track or in-line legged mobile robot movingforward and shifting the center of pressure to along the zero momentline that bisects the centers of the front foot and rear foot to affordthe legged mobile robot to lift the middle foot while maintainingstability of balance in a biped stance;

FIG. 20 illustrates a top schematic view illustrating center of gravity,placement of the feet, and resulting area of support for the singletrack or in-line three legged mobile robot illustrated in FIG. 19;

FIG. 21 illustrates the middle foot contacting the ground, and a singletrack or inline legged mobile robot reestablishing the triangularthree-point contact support pattern;

FIG. 22 illustrates a top schematic view illustrating center of gravity,placement of the feet, and resulting area of support for the singletrack or in-line three legged mobile robot illustrated in FIG. 21;

FIG. 23 illustrates a single track or in-line legged mobile robot movingforward and shifting the center of pressure to along the zero momentline that bisects the centers of the front foot and middle foot toafford the legged mobile robot to lift the rear foot, while maintainingstability of balance in a biped stance;

FIG. 24 illustrates a top schematic view illustrating center of gravity,placement of the feet, and resulting area of support for the singletrack or in-line three legged mobile robot illustrated in FIG. 23;

FIG. 25 illustrates the rear foot contacting the ground, and a singletrack or inline legged mobile robot reestablishing the triangularthree-point contact support pattern;

FIG. 26 illustrates a top schematic view illustrating center of gravity,placement of the feet, and resulting area of support for the singletrack or in-line three legged mobile robot illustrated in FIG. 25;

FIG. 27 illustrates the lifting of the body and repositioning of themiddle leg in preparation to begin a walking cycle;

FIG. 28 illustrates a top schematic view illustrating center of gravity,placement of the feet, and resulting area of support for the singletrack or in-line three legged mobile robot illustrated in FIG. 27;

FIG. 29 illustrates a perspective skeletal view of a single track orin-line three legged mobile robot executing a single-track leaning turn;

FIG. 30 illustrates a parabolic shaped foot to maintain constant surfacearea contact with the ground during a single-track leaning turn;

FIG. 31 illustrates a schematic skeletal view of a single leg ofillustrating the fundamental feedback and control system of a singletrack or in-line multi legged mobile robot;

FIG. 32 illustrates a data flow model of an example control system forthe in-line multi legged mobile robot.

FIGS. 33A-33B illustrates lateral sectional views of a single track orin-line three legged mobile robot, where FIG. 33A illustrates the robotwith rider, and FIG. 33B illustrates the resulting free body diagram;

FIG. 34 illustrates a front view of a single track or in-line threelegged mobile robot extending a leg in the direction of roll to catchits fall;

FIG. 35 illustrates an example of a wave gait diagram for a single trackor in-line three legged mobile robot with a 10111 support phase and 1111swing phase;

FIG. 36 illustrates an example of a backward wave gait diagram for asingle track or in-line three legged mobile robot with a 5/6 stance and1/6 flight phase;

FIG. 37 illustrates an example of a backward wave gait diagram for asingle track or in-line three legged mobile robot with a 2/3 stance and1/3 flight phase;

FIG. 38 illustrates an example of a backward wave gait model for asingle track or in-line three legged mobile robot with a 5/6 stance and1/6 flight phase where the swing cycles are grouped together;

FIG. 39 illustrates an example of a backward wave gait model for asingle track or in-line three legged mobile robot with a 8/11 stance and3/11 flight phasing with two intervals where all three legs aresimultaneously supporting the body;

FIG. 40 illustrates an example of an equal phase backward wave gaitmodel for a single track or in-line three legged mobile robot;

FIG. 41 illustrates an example of a variation on an equal phase backwardwave gait model for a single track or in-line three legged mobile robot;

FIG. 42 illustrates an example of a variation on an equal phase backwardwave gait model for a single track or in-line three legged mobile robot;

FIG. 43 illustrates an example of a variation of a 2/3 stance and 1/3flight backward wave gait for a single track or in-line three leggedmobile robot, wherein affordance is given to reposition the middle legduring the front and rear leg support;

FIG. 44 illustrates an example of a variation of a 2/3 stance and 1/3flight backward and forward wave gait for a single track or in-linethree legged mobile robot, wherein affordance is given to reposition themiddle leg to accommodate changes in front and rear leg stance;

FIG. 45 illustrates an example of a fast trot gait combined with ahopping model for a single track or in-line three legged mobile robot;

FIG. 46 illustrates an example of a running gait for a single track orin-line three legged mobile robot;

FIG. 47 illustrates an example of a pronking gait for a single track orin-line three legged mobile robot;

FIG. 48 illustrates an example of a bounding gait for a single track orin-line three legged mobile robot;

FIG. 49 illustrates a side skeletal view of a single track or in-linethree legged mobile robot illustrating a bounding takeoff; and

FIG. 50 illustrates a side skeletal view of a single track or in-linethree legged mobile robot illustrating a bounding landing.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be explained with reference to a single track orin-line three legged mobile robot as a specific embodiment of the singletrack multi-legged mobile robot. Referring now to the drawings and, moreparticularly, to FIGS. 1-3 thereof, there is shown a single track orin-line legged mobile robot, generally designated 41, including a bodyor frame, generally designated 42, and three identical leg mechanisms,generally designated 43, attached one behind the other, substantiallyparallel to the major axis of the frame 42, defining a forward/backwarddirection of travel along planes 44 and 55. By convention, the left sideof the page is the front side and forward direction, the right side ofthe page is the rear side, into the page is the right side, and out ofthe page is the left side of the robot 41. The construction of each legmechanism 43 is not directly relevant to the present invention, thepresent invention being directed to the method and manner in which theleg mechanisms 43 may be combined and attached to the body 42 forforming a complete legged mobile robot and control thereof. However, legmechanisms 43 will be described briefly, because the teachings of whichare necessary for an understanding of the present invention. Since eachleg mechanism 43 a, 43 b, and 43 c is identical, a description of onewill suffice to describe all.

It will be readily apparent by those skilled in the art, from aninspection of the drawings that a pantograph leg, as illustrated in FIG.1, is a preferred embodiment. A pantograph leg mechanism would include aplurality of elongated links arranged in a parallelogram to form apantograph mechanism whereby forces applied at selected points onindividual parts of the links can be transmitted to another link whichforms the movable foot 45 a-45 c of the mechanism, or a movable distalend of a leg 43 a-43 c. Vertical movement of foot 45 a-45 c iscontrolled by a sliding or prismatic actuators 10 a-10 c orientedvertically, horizontal movement of the foot 45 a-45 c is controlled by asliding or prismatic horizontal actuator 11 a-11 c, lateral or outwardmovement of the foot 45 a-45 c is controlled by the rotational actuator12 a-12 c, wherein the horizontal and vertical mechanism is mounted forrotation with respect to the body 42. Actuators 10-12 may be electricmotors, electro-hydraulic servos or other known technologies suitablefor accurately effecting the movement of the legs 43 and other jointedmembers. Pantograph legs, as illustrated in FIG. 1, reduce thecomplexity of actuation, increasing reliability, and decreasingcomputational requirements. However, the popularity of biologicallyinspired jointed legs, found in prior art and in commercialoff-the-shelf robotic kits is believed to improve the clarity ofunderstanding the teachings.

An overall skeletal view of the tri-legged walking machine is shown inFIGS. 2-3. The articulated structure of the legged walking machine 41includes three jointed legs mounted in-line, one behind the other, alongthe length of the body 42 such that the three legs establish a plane 44(X-Z axis). Each leg mechanism is associated with six articulations orjoints (axes) to enable each foot 45 a, 45 b, and 45 c to be positionedin six dimensions (X-Y-Z and roll-pitch-yaw axis, respectively) withrespect to the body 42. Since each leg mechanism 43 a, 43 b, and 43 c isidentical, a description of the first leg 43 a will suffice to describeall and the other legs are unlabeled for clarity. The joints (axes) ofthe leg include a yaw rotational joint (yaw axis) 46 a for turning theleg and foot 45 a with respect to the body 42, a roll rotational joint(roll axis) 47 a for moving the foot to the side (Y axis) of the body42, a pitch rotational joint (pitch axis) 48 a on a thigh link 49 a formoving the foot forward and backward (X axis), a rotational joint (axis)50 a in the knee and at the distal end of the thigh link 49 a and on ashank link 51 a for moving the foot forward and backward (X axis), arotational joint (axis) 52 a at the distal end of the shank link 51 afor moving the foot in the pitch direction, and a rotational joint(axis) 53 a for moving the foot in the roll direction. Axes 52 and 53are parallel to the pitch and roll axes, respectively. The foot 45 a ismounted to a small shank (not labeled for clarity) connected torotational joint 53 a on the lower end of the leg 43 a. The joints(axes) 46, 47, and 48 jointly constitute a hip joint assembly, joint 50constitute a knee assembly, and the joints 52 and 53 jointly constitutea foot joint assembly. The foot 45 is moved forward or backward withrespect to the length of the body 42 or parallel to the plane 44 byrotating joints 48, 50, and 52 and/or rotating joints 23. The foot 45 ismoved to the right or left side with respect to the length of the body42 or perpendicular to the plane 44 by rotating joints 47 and 53 and/orrotating joints 21. The foot 45 is rotated clockwise or counterclockwisewith respect to the length of the body 42 by rotating joints 46 and/orrotating joints 22. The roll axis 54 of the walking machine 41 is aboutankle joints 53. Note that for legs with a point-contact foot, that iswithout ankle joints 53, the roll axis 54 is at the point of contact ofthe at least two single track feet 45 and the ground 55 for thecondition where there is negligible foot slip. It may be desirable forlegs 43, connecting joints 21-23 and/or feet 45 to be mechanicallycompliant to comprise a spring-mass-damper system to afford a gentlerride of body 42.

Still referring to FIGS. 2-3, body 42 includes three main support platesto mount the legs 43 to frames 56 and 57 on body 42 to afford roll,pitch, and yaw hip rotations along the axis of motion such that the footmay be positioned laterally or radially outward with respect to the body42 and measured thusly. On each of the thigh and the ankle of each leg,the pitch joints 48 and roll joints 47 are disposed perpendicularly toeach other, and have respective axes intersecting with each other at onepoint. The joints 48, 50, and 52 in the hip joint assembly, the kneejoint, and the foot joint assemblies, respectively, extend parallel toeach other in plane 44. Irrespective of movements caused by otherdegrees of freedom, particularly, movements of the joints 46 to changethe direction of the legs, the joints 48, 50, and 52 remain parallel toeach other, with respect to a single leg. In the hip joint assemblies,the joints 46 and the pitch and roll joints 47, and 52 extendperpendicularly to each other, so that the three axes of rotation,representing three degrees of freedom, extend perpendicularly to eachother. More specifically, the axis 46 may be considered to define afirst axis of the hip joint assembly, the axis 47 to define a secondaxis of the hip joint assembly, and the axis 48 to define a third axisof the hip joint assembly. The axes 46, 47 and 48 each providerespective degrees of freedom about which the leg of the robot may bemoved, for example, the axis 48 provides a first degree of freedom forangularly moving the leg forwardly in the pitch direction, the axis 47provides a second degree of freedom for moving the leg laterally in theroll direction, and the axis 46 provides a third degree of freedom inthe yaw direction for rotating the leg with respect to the body 42. Itshould be understood, however, that the designations “first,” “second”and “third” are arbitrary, and are used merely to facilitate adescription of the invention. The legs 43 thus have six degrees offreedom each, so that during locomotion the legs as a whole can becaused to execute the desired motion by driving the 6×3=18 joints (axes)to appropriate angle. Irrespective of the position or posture of thebody 42, the feet 45 can be placed in any position, at any angle, and inany direction. The robot is thus capable of walking freely within threedimensional space. The joint actuations may be provided by any meanssuch as electric motors and reduction gear mechanism for increasingmotor torque or high pressure servo hydraulics. A power supply 13 and acontrol unit 86 are mounted on the legged vehicle. The power supply isin communication with each component of the legged vehicle whichrequires power, including the control unit 86 and all its distributedcomponents, and the numerous actuators. The control unit 86, also calleda control system in a larger sense, includes numerous parts, asdescribed above, including numerous sensors which may be distributedthroughout the vehicle.

Still referring to FIG. 1-3, body 42 has physical mass and thus a centerof gravity 58 and its projection to the ground 55, called the center ofpressure 59. The center of gravity 58 and center of pressure 59 are wellknown physical properties, especially with respect to single trackvehicles, such as motorcycles and bicycles, legged mobile robots and thelike, described in the prior art.

Referring now to FIGS. 4-8, several views of possible configurations ofthe legs and the method in which operation of the individual legs moveare illustrated, whereby foot placement along the length of the body 42and in the major direction of motion shall now be discussed. Accordingto the preferred embodiment of the present invention, each leg 43 can berotated about hip, knee, and ankle joints in three dimensions. FIG. 4illustrates the side skeletal view of one possible configuration of thelegs, wherein the x and z axes with the side or y axis into and out ofthe page. By convention, the left side is the forward direction. Thefirst leg 43 a is shown with its foot 45 a extended forward with respectto its hip joints 46 a, 47 a, and 48 a. Hereinafter, the terms forwardor rearward shall be with respect to the hip joints 46, 47, and 48 alongthe length of the body 42. The second or middle foot 45 b is shown in amiddle or neutral position, and the third foot 45 c is shown in arearward extended position. From left to right, the first dashedcardioid 61 a envelops and illustrates the total range of motion for thecenter bottom of foot 45 a (hereinafter the center bottom of each footis referred to as the foot), and a second rectangular dashed box 62 ainscribed inside the first dashed cardioid 61 a and illustrates theworking range of motion for foot 45 a. Two more dashed cardioids 61 band 62 c and two more dashed boxes 62 b and 62 c illustrate the totalrange of motion and working range of motion for feet 45 b and 45 c,respectively. In operation, FIG. 4 shows the range of motion for eachfoot 45 of each leg 43 wherein there is a maximum working envelope 61and a typical working range 62 for legged locomotion. Both the maximumworking envelope 61 and typical working range 62 are three-dimensionalvolumes, but are shown as two-dimensional areas for clarity. Because theleg system shown uses hip, knee, and ankle joints, as previouslydescribed, the maximum working envelopes 61 is unique for that leggeometry. It would be different for pantograph legs of FIG. 1, forexample.

Specific to this invention is the overlap of the typical working range62 a, 62 b, and 62 c, shown as a dashed rectangular boxes within themaximum working envelope 61 a, 61 b, and 61 c, shown as dashedcardioids, because it is highly desirable to have a legged mobile robotwhich can operate on uneven surfaces, such as along narrow trails andpaths, for example those found in parks and wilderness areas. That is,at a minimum the maximum working envelope 61 a overlaps with 61 b, and61 b overlaps with 61 c, and at a minimum the typical working range 62 aoverlaps with 62 b, and 62 b overlaps with 62 c. In other words, thetypical working range of the front leg overlaps with the middle leg andthe middle leg overlaps with the rear leg to enable in three dimensionsthe front foot 45 a to be positioned alongside the middle foot 45 b andthe middle foot 45 b to be positioned alongside the rear foot 45 cwithout mechanical interference. FIG. 5 schematically shows athree-dimensional perspective view of a leg configuration wherein eachfoot is displaced to left or right side of the projected center ofgravity such that feet 45 a and 45 c traverse a centerline 64 that isspatially displaced but parallel to the centerline 65 of foot 45 b. FIG.6 schematically shows the top view of FIG. 5 wherein the centers of feet45 are shown as dots, displaced about the center of gravity 58 and itsground projection center of pressure 59 (not shown for clarity) of body42. FIG. 5 schematically shows one possible configuration of the legs 43of the legged mobile robot 41 in a resting stance configuration, such aswhen the robot is turned off, of the foot 45 placement and leg 43geometry such that the legs are in a tripod configuration and the leggedmobile robot does not fall over.

FIG. 7 schematically shows a side view where the front leg 43 a is fullyextended rearward and the middle leg 43 b is fully extended forward.FIG. 8 schematically shows the top view of FIG. 7 wherein the centers offeet 45 are shown as dots, displaced about the center of gravity 58 andits ground projection center of pressure 59 (not shown for clarity) ofbody 42. The legs 43 and feet 45 may be configured in infinite varietysuch that the projected center of gravity 58, the center of pressure 59,is contained within the foot extent. In terms of the zero moment point(ZMP), the feet 45 are positioned such that the net moment or torqueabout the projected center of gravity 58, the center of pressure 59, iszero and the robot does not fall down. The advantage of such a range ofmotion can be seen in FIG. 8, wherein the extreme rearward position ofthe front leg 43 a and the extreme forward position of middle leg 43 boverlap such that the feet 45 a and 45 b are positioned similar to thatof a biped. This design and method is highly important so that a leggedmachine can achieve the desired stability of balance, leap and jump,land, and so on, and in addition to the legs 43 being capable ofoperation in such a manner that it has a very narrow profile so that itcan maneuver in a space where walking machines previously could not go,such as along a narrow path or trail or through a door.

Referring now to FIGS. 9-28, the single track or in-line legged mobilerobot 41 is shown in side views and top views traversing a vertical orstep gradient 66 to illustrate certain properties of the invention, suchas for example adjusting the walking height and/or body attitude on agradient, the horizontal range, the vertical range, maintaining balanceon three legs, maintaining balance on three legs, and a lateralside-step or shuffle maneuver. Such properties of the invention arefundamental to traversing uneven or rugged terrain, ditch crossing, wallcrossing, climbing, and so on. Starting with FIG. 9, the legged mobilerobot 41 illustrates one possible configuration of legs 43 and foot 45placement before traversing the vertical or step gradient 66. FIG. 10shows a top view schematic of the ground 55 illustrating placement ofthe feet 45 with respect to the body 42, x-z reference plane 44, andprojected center of pressure 59. By convention, the left side is theforward direction.

Next, FIGS. 11-12 show the single track or in-line legged mobile robot41 adjusting the walking height and/or body attitude in preparation totraverse the vertical or step gradient, by dropping the rear portion ofbody 42. This maneuver has the effect of shifting the projected centerof pressure 59 rearward such that it intersects with a zero moment line25 bisecting the centers of the middle foot 45 b and rear foot 45 c. Atthis time, the legged mobile robot 41 is effectively in a biped stance.Also the working range of motion for each foot 45 has shifted. The frontfoot 45 a is now positioned at the lowest and most rearward position ofthe working range 62 a, the front portion of the working range 62 a hasrisen off the virtual ground plane of the lower ground 55, the middlefoot 45 b and rear foot 45 c are within their working ranges 62 b and 62c, respectively, and the rear portion of the working ranges 62 b and 62c have sunk below the virtual ground plane of the lower ground 55. Notethat there is still some margin between the working range 62 a and themaximum working envelope 61 a (not shown for clarity) to provide asafety margin for external dynamic events, such as a force imparted by arider or the wind.

Next, FIGS. 13-14 show the single track or in-line legged mobile robot41 lifting itself on the middle and rear legs 43 while simultaneouslylifting the front foot 45 a off the lower ground 55 and repositioning itbeyond the vertical or step gradient 66 to be above the upper ground 55.Feet 45 b and 45 c are in a bipedal-like stance along the zero momentline 25 intersecting the center of pressure 59. Lifting the body 42 isnecessary to raise the working range 62 a to above the level of theupper ground 55. The body 42 is lifted vertically until the middle foot45 b reaches the bottom of the working envelope 61 b. Note again thatthere is still some margin between the working range 62 b and themaximum working envelope 61 b (not shown for clarity) to provide asafety margin for external dynamic events, such as a force imparted by arider or the wind. This note is typical for further maneuvers and willnot be re-noted for readability. FIGS. 15-16 shows the single track orin-line legged mobile robot 41 shifting its body 42 and thus itsprojected center of pressure 59 on the middle and rear legs 43 to movethe body 42 and thus the front foot 45 a forward, while maintainingbalance by keeping the center of pressure 59 along the zero moment line25 that bisecting the centers of the middle foot 45 b and rear foot 45c. Note that in the case where all three legs are in contact with theground, as in the stance phase of a wave gait, a similar shift of thebody 42 is used to maintain balance, and the legs 43 may be successivelyrepositioned in a similar manner such that the body 42 moves sideways.This method of shifting the body 42 and legs 43 allows the legged mobilerobot 41 to move omnidirectionally. FIGS. 17-18, and in particular FIG.18, show the single track or in-line legged mobile robot 41 placing thefront foot 45 a on the upper ground 55 and reestablishing the triangularthree-point contact support pattern. At this time, any dynamicinstability arising from, for example, measurement errors or externaldynamic forces, acting on the bipedal stance are counteracted or resetby the more supportive tripod stance.

Next, FIGS. 19-20 show the single track or in-line legged mobile robot41 moving forward and shifting the center of pressure 59 to along thezero moment line 26 that bisects the centers of the front foot 45 a andrear foot 45 c to afford the legged mobile robot 41 to lift the middlefoot 45 b while maintaining stability of balance by the front leg 43 aand rear leg 43 c in a biped stance. Note that in any dynamic system,the momentum imparted by moving the body 42 forward and shifting istaken into account by the control unit 86 such that the middle leg maybe lifted off the ground sooner than the static case of when the centerof pressure 59 must reach the zero moment line 26 that bisects thecenters of the front foot 45 a and rear foot 45 c to maintain staticstability of balance. As such, the center of pressure may only approachthe zero moment lines 25, 26, 29 but may not reach it before subsequentfoot steps are made. The middle foot 45 b is positioned above the upperground 55 and forward of the vertical or step gradient. FIGS. 21-22 thenshow the middle foot 45 b contacting the ground, and the single track orin-line legged mobile robot 41 reestablishing the triangular three-pointcontact support pattern. At this time, any dynamic instability arisingfrom, for example, measurement errors or external dynamic forces, actingon the two-leg, bipedal stance are counteracted or reset by the moresupportive tripod stance.

Next, FIGS. 23-24 show the single track or in-line legged mobile robot41 moving forward and shifting the center of pressure 59 to along thezero moment line 27 that bisects the centers of the front foot 45 a andmiddle foot 45 b to afford the legged mobile robot 41 to lift the rearfoot 45 c while maintaining stability of balance by the front leg 43 aand middle leg 43 b in a biped stance. The body 42 is rotated to a levelposture while rear foot 45 c is simultaneously positioned above theupper ground 55 and forward of the vertical or step gradient. FIGS.25-26 then show the rear foot 45 c contacting the ground, and the singletrack or in-line legged mobile robot 41 reestablishing the triangularthree-point contact support pattern. At this time, any dynamicinstability arising from, for example, measurement errors or externaldynamic forces, acting on the two-leg, bipedal stance are counteractedor reset by the more supportive tripod stance.

Next, FIGS. 27-28 show the lifting of the body 42 and repositioning ofthe middle leg 43 b in preparation to begin a walking cycle on the upperground 55. The body 42 is shifted such that the center of pressure 59 isrepositioned to along the zero moment line 28 that bisects the centersof the front foot 45 a and rear foot 45 c to afford the legged mobilerobot 41 to lift the middle foot 45 b while maintaining stability ofbalance by the front leg 43 a and rear leg 43 c in a biped stance. Thelegged mobile robot would then shift the center of pressure 59 over toalong or near the zero moment line 29 that bisects the centers of themiddle foot 45 b and rear foot 45 c and reposition the front foot 45 ato the forward most position while simultaneously moving the body 42forward. Forward motion is then maintained by any number of gaits, suchas for example a backward wave gait, discussed later.

Referring now to FIGS. 29-30 and as was previously mentioned, dynamicmomentum plays an important role in maintaining the stability of balanceof dynamic or moving systems. Like wheeled motorcycles and bicycles,FIG. 29 shows the legged mobile robot 41 executing a single-track turnwhereby the body 42 is spatially and angularly displaced from the normalplane of operation 44, called “leaning into the turn”, such that thecenter of gravity 58 and projected center of pressure 59 is movedtowards the center of curvature 70 thus developing a torque about theroll axis 54 (not shown for clarity but refer to the feet 45) thatcounteracts the outward centripetal inertial force acting on the centerof gravity 58 of the body 42. In leaning into a turn, the feet 45 arefollowing a single track or in-line curve 71 of radius 72 about thecenter point 70 normal to the ground 55, and the body 42 is leaning withangle theta 73 between the normal reference plane 44 and the projectedplane 74 tangent to the single track or in-line curve 71 on the ground55 and through the center of gravity 58 and parallel to the body 42length. The top of the body thus follows a second curve 75 of smallerradius 76 about the projected center point 70 normal to the ground suchthat the resulting plane of motion 77 is a truncated cone. The leggedmobile robot 41 is able to lean into a turn like wheeled motorcycles andbicycles but with the advantage of a narrow profile along the directionof motion and the ability to choose discrete foot holds for the feet 45.This design and method is highly important so that a legged machine canachieve a high-speed turn and dynamic turns over rugged terrain notheretofore accomplished by legged mobile robots.

Referring again to FIG. 29, forward motion is achieved by any number ofgaits, such as for example a wave gait, discussed later, whereby eachfoot 45 is repositioned along the desired single track or in-line curve71 with minor variation in radius 72 to achieve stability of balance. Amore aggressive gait, such as for example the leg crossover motion usedby ice skaters where curve 71 is a piece-wise combination of curves ofdifferent radius and center point to achieve the overall desired motionof body 42. Such aggressive gaits would find use on lose ground orslippery surfaces, because for each piece-wise curve each leg 43 wouldnot only develop an outward torque in the direction of slip that wouldfurther counteract the outward centripetal inertial force acting on thecenter of gravity 58 of the body 42 but would incrementally push thebody 42 in the desired direction of motion. Furthermore, if bottoms ofeach of the feet 45 were ice skating blades, a piece-wise curve woulddevelop force in the forward direction to propel the legged mobile robot41 in the forward direction.

Referring now to FIG. 30, it will be readily apparent by those skilledin the art, from an inspection of the drawings, that the feet 45 neednot be positioned co-planar with the ground using an ankle mechanism 52and 53. Rather, FIG. 30 illustrates the front view, in both the left andright sides, a preferred embodiment of the foot 78 wherein the shape ofthe lateral (the axis perpendicular to the major direction of travel)cross section of the foot is parabolic 79 to maintain constant surfacearea contact with the ground as the single track or in-line leggedmobile robot 41 is leaned into the turn (illustrated right). Further, asemi-rigid but elastically compliant material, such as rubber, may beused for the foot surface 80 to further improve contact surface areabetween the robot foot and ground, especially given any naturallyoccurring minor surface irregularities.

Referring now to FIGS. 31, 32, 33A and 33B, the individual ankles 52 and53 of the leg 43 of the legged mobile robot 41 are shown with a sixdimensional force and torque sensor 81 of conventional design. Bymeasuring the x, y and z force components Fx, Fy and Fz transmitted tothe legged mobile robot 41 through the feet 45 and also measuring themoment components Mx, My and Mz around the three axes, thesix-dimensional force and torque sensor 81 detects whether or not theassociated foot 45 has landed and the magnitude and direction of theforces acting on the supporting leg 43. The body 42 may be provided witha three-dimensional inclination sensor 82, called an inertialmeasurement unit or IMU, rigidly connected by mount 83 that isultimately connected to leg mounts 56 and 57, not shown for clarity. TheIMU is sometimes also referred to as an inertial navigation system orINS. An INS combines the IMU with complementary filters and kinematicproprioceptive information (body height, center of pressure, zero momentpoint, etc.) to provide more accurate dynamic information. The IMU 82measures the robot's three-dimensional (roll, pitch, and yaw) angle,angular velocity, and angular acceleration relative to z axis in the x-zreference plane 44, y-z plane, and ground (x-y) plane 55, not shown forclarity.

Accurate sensing of roll angles and angle rates is required to balancethe present invention. Most known methods to balance legged or invertedpendulum type mobile robots uses gyroscopes, accelerometers, tiltsensors, and potentiometer or encoder-based leg joint angle measurement.A sensor fusion approach may be used for computing absolute orientationand rotation in real-time by combining angle rate data from amicro-electro-mechanical systems vibrating structure gyroscope, or MEMSgyro for short, with absolute angle data from statistical imageprocessing of a visual scene. A Kalman filter is used to fuse and smoothmultiple sensor input. The accuracy of the combined system exceeds thatof either sensor used alone. MEMS Gyro drift error may be compensatedwhile preserving a high response rate.

In one embodiment and referring to FIGS. 31 and 32, the presentinvention uses a model-based predictive control system for mobile robotbalance and path planning The system includes a camera module 30 mountedto the frame 42 for sensing distant objects and image processor module31 for analyzing road preview data corresponding to the spatiallocations of foothold areas located ahead of the robot. The footholdareas are tracked using a temporal tracking module 32 that uses jointand body angles and rates from sensor 97, 99, and 100, mounted to frame42, processed by a forward kinematics module 33 to determine thesix-axis body position, velocity, and acceleration 34. A control signalcomprising steering angle, forward velocity, and vehicle height is inputvia a operator input module 35 to a gait coordination module 36 andhigh-speed model 37. The gait coordination module 36 coordinates thelegs/feet motion based on predicted future locations of foothold areas,predicted future robot balance or stability state, and the desired orcontrol command from the high-speed model 37. The high-speed modelmodule 37 is operatively coupled 38 to the gait coordination module 36,the forward kinematic module 33, and the leg state machine module 39 tofacilitate real-time control. The leg state machine 39 also receivesdata from the forward kinematics module 33 and reports real-time legstates to the gait coordination module 36. The tracking system module 32is configured to predict estimated future locations of the at least onefoothold area to simulate multiple robot motion hypothesis for leg/footplacement and trajectory planning in the high-speed model module 37. Thehigh-speed model module 37 operates faster than real-time to enablerobot state preview, with respect to all measurable movement andpositioning parameters of the robot, given the initial conditions(real-time) of the six-axis body position, velocity, and acceleration34. The control algorithm may use probabilistic modeling and simulationto produce temporal-based foot trajectory planning action commands tocontrol and coordinate the legs, all in the presence of missing data,latency, translational bias, and/or sensing error.

The high-speed model module 37 predicts a future position or staterather than only using the current-time measurements of the robot. Forexample, while reactively adjusting step length for the availablefootholds, forward speed, body height, and duration of ground contactmay also be controlled to actively balance legged mobile robot. Thelegged mobile robot control system may also account for rider-inducedperturbations (especially in the roll axis) and mechanical losses in thesystem.

To implement real-time motion, the future leg state commands from thehigh-speed model module 37 are verified and validated by the leg statemachine module 39 using a fundamental leg four-state cycle modelcomprising: 1) developing reaction forces, torques, and thrusts in astance phase wherein leg/foot-to-ground interaction is transferredthrough the leg to stabilize the frame in the pitch, roll, and yaw axesand to propel the frame in the x, y, and z axes, respectively, thefoot/distal end of the leg being generally stationary with respect tothe ground during the stance phase and moving generally opposite to themajor direction of frame motion, of a monopedal stance, a bipedal stanceand a tripedal stance, according to the control system; 2) unloadingreaction forces through the leg/foot in a stance-to-flight phase whereinthe foot is lifted off the ground, controlling leg velocities, accordingto the control system; 3) repositioning the leg/foot in a flight phasewherein the distal end of the leg/foot is moved generally in the samedirection as the frame and generally at a faster rate, relative to theground, as the major direction of frame motion, controlling footplacement and leg movement to maintain an upright posture and meet footplacement constraints and desired trajectory requirements for the frameand legged vehicle, according to the control system; and 4) placing theleg/foot to the ground and developing reaction forces, torques, andthrusts in a flight-to-stance phase. A servo control module 40implements real-time leg position, velocity, and acceleration commandsto the actuator system 98, mounted to frame 42 to produce useful work.

It is an object of the present invention to solve the problemsassociated with performing a lean-into-a-turn maneuver (with respect tothe body and primary direction of motion) using the single track orin-line multi-legged mobile robot design. In solving this problem, amodel-based predictive control system robotic control system may be usedto provide autonomous attitude stabilization control. In the case whereall three legs are in contact with the ground, as in the stance phase ofa wave gate, the ability to shift one of the legs laterally to affectbalance is an advantage or result.

Still referring to FIG. 31, each actuator at the individual joints 46,47, 48, 50, 52, and 53 is provided with an encoder disposed adjacent tothe respective motors for generating sensed kinematic data for actuationcontrol, proposition and posture. As illustrated in FIG. 31, the leggedmobile robot 41 is provided with a zero reference switch 84, such as anoil-damped pendulum, for calibrating the output of the IMU 83 and alimit switch 85 for a failsafe to stop motion in the case of overturn.The outputs of the sensors 81, 82, 83, and 85 are sent to the controlsystem 86. The control system 86, which may be synonymous with thecontrol system, is a computer comprising the at least one centralprocessing unit or CPU 87, read only memory or ROM 88, random accessmemory or RAM 89, data storage 90, such as for example a solid statedrive, and input output devices including but not limited to digital toanalog converter or D/A 91, digital counter 92, digital interface 93,such as for example a universal serial bus or USB port, analog todigital converter or A/D 94, and network interface 95, such as forexample an Ethernet port. All aforementioned devices are connectedtogether by the at least one bus 96. The angle, angle rate or velocity,and angle acceleration 97, from the inclination sensor 83 iscommunicated to the control unit 87 via the digital interface 93. TheD/A output 91 is amplified 98 to control joint actuators 46, 47, 48, 50,52, and 53 with resulting encoders provide joint angle feedback 99converted into digital signals by counter 92. Feedback 100 from sixdimensional force and torque sensor 81 is input to the A/D 94. Theresulting digital values are sent via a bus 96 to RAM 89 for storage.

In a preferred embodiment, the control unit 86 is a low-level orreal-time processor primarily responsible for dynamic actions withrespect to the ground reaction force, the reaction force produced fromgravitational forces and inertial forces. The term “ground reactionforce” is used here to mean the resultant force and moment at a point ofaction obtained as the vector sum of all ground reaction forces actingon the individual legs 43. Specifically, the control unit 86 isresponsible for planning and reacting to mechanical feedback, calledpreflex-dominated control. A preflex is defined as the zero-delay,intrinsic response of a neuromusculoskeletal system to a perturbationand is programmable via pre-selection of muscle activation. Leg preflex,for example, pulls the foot back and lifts it if the force and torquesensor 81 of foot 45 indicates it encounters an unexpected obstacleduring a flight phase. Leg pre flex, also for example, causes the leg topush downward if the force and torque sensor 81 of foot 45 indicatesthat it is not bearing adequate vertical load during touchdown (flightto support transition) or during stance (as in loose ground). Leg preflex, also for example, causes the relative leg length to be adjusted sothe body remains level. These are feed-forward control process, and therobot is stable when the forces acting on it are in dynamic equilibrium.

For realizing preflex-dominated control, the invention provides animproved model-based control system for a legged mobile robot having theat least one model which the control follows. A target gait defines theexpected ground reaction force so as to ensure a state of dynamicequilibrium based on the robot's dynamic model, wherein the improvementcomprises that manipulated variables are a function of state errors,such as for example where the inclination of the model and the actuallegged mobile robot is fed back to the at least one model for modifyingits behavior. In this technique, the CPU 87 fetches the at least onemodel stored in ROM 88 as the basis for coordinating the movement of thevarious legs 43 and computing target joint angles (joint drive patterns)for legged gaits and behaviors, and various leg stances andtrajectories, described later. The actuation signals 98 are thencomputed using the roll, pitch, and yaw torque sensors 81 andthree-dimensional angle, angle rate, and angle acceleration feedbackfrom the IMU sensor 82 stored in RAM 89. The CPU 87 calculates thedesired actuator positions based on a dynamic model and the feedback toconverge to zero the error, and to account for sensor and measurementerror and the dynamic nature of the environment, such as for example,unexpected forces imparted to the body 42 by the at least one rider orpassenger 101 over rugged and loose terrain. For example, the CPU 87thus calculates the shift of ground reaction force of the model in thedirection to which the attitude is restored, and the control unit 86thus drives the actuators to eliminate differences between the presentangular positions and the control values. Thismodel-to-actuation-to-feedback is called closed loop control.

In cases where the ground configuration is known and little disturbancearises owing to ground irregularities (bumps and recesses) or in caseswhere compliance is achieved mechanically, there is no particular needto conduct the ground reaction force feedback control. Even if it is notconducted, there is no loss of the advantage of the invention. Forexample, the spring loaded inverted pendulum (SLIP) model for leggedlocomotion is known. SLIP applies to an elastic leg serving to store andreturn energy during the course of the stance phase. While locomotionover uneven terrain would seem to require significant feedback control,actuation is prescribed in a feed-forward manner. Traditionally, manyemploy variations of Raibert's original idea of energy addition throughthrust timed with the point of maximal leg compression. However like amotorcycle, simple forward foot placement strategy is all that isneeded. That is, a leg that misses the ground would continue to react,exhibiting actuation similar to those employed by legs in contact withthe ground. For example, running guinea fowl recover form an unexpecteddrop by posture-dependent leg actuation where both changes in leg lengthand leg angle at touchdown, with relative stretch and leg angle attouch-down governing the sign and magnitude of energy addition/removalduring the stance phase. For example, cockroaches running over roughterrain are shown to appropriately reorient the system momentum inresponse to external perturbations, thereby improving stability of thevelocity heading angle.

For effective dynamical legged locomotion, the actuation protocol isfeed-forward with limited sensing (rather than high-bandwidth feedbackcontrol), similar to the consistent muscle activation patterns observedin cockroaches running over rough terrain, with variations of legtouch-down angle incorporated based on posture-dependent leg actuationfor improving stability of the velocity heading angle. Leg touch-downangle is prescribed using the SLIP model based on leg angles used in theprevious stance phase. Swing-leg retraction actuates the leg at aconstant angular velocity from the apex of the flight phase.Perturbations from a periodic body orbit cause variation in legtouch-down angle.

When a large disturbance is applied, one or more legs 43 may berepositioned to counteract the force. The pitch angle and angularvelocity of the body 42 is measured using the IMU 83 combined withcomplementary filters and kinematic proprioceptive information (bodyheight, center of pressure, zero moment point, etc.). The angularsideways velocity and angular sideways displacement of the leg 43 may bemeasured with rotary encoder 99. Using said feedback, the control input,u, may be modeled.

Furthermore, the LRQ method is known and may be used to balance systemerrors with control. For example, if the weighting factors for the hipsideways velocity and displacement are increased, the system becomesvery sensitive to disturbance, but more accurate path tracking isobtained. If the weighting factors for the hip sideways velocity anddisplacement are increased, the system becomes less sensitive todisturbance and less accurate path tracking is obtained, requiring moreleg/foot repositioning.

The body 42 leans in the direction from which the external force isapplied. Full-state feedback may be used to control the stabilization ofthe upright equilibrium or balance, and a reduced-order disturbanceobserver estimates the external force. Through the use of estimatedexternal forces, the hip torque and/or leg/foot repositioning occurs.Further refinement of control considers the steering angle and thedriving torque. Insofar as a model which faithfully simulates thedynamics of the actual robot is created and the difference between theground reaction force of the actual robot and that of the robot model iscontrolled, the same principle can be applied with the same effectirrespective of the number of single track or in-line legs.

Road Preview through Rider Cues

Controlling a robot while riding the robot necessitates methods forcommanding the robot, such as through body language (e.g., shiftingweight), verbal commands, and via a control interface (e.g., handle barsand hand-grip controls). Body language or behavioral cues or any actionor signal that a rider's current actions (e.g., body language, verbalcommand, look direction, etc.) may provide clues or cues for the controlsystem as to the actions the operator desires the platform to do in thefuture.

To complement the basic predictive control system, a robot mountedcamera may be used to observe the rider, a vision system may be used tomeasure the behavioral cues, and a Kalman filter may be used to fuse andpredict such cues. The controller continuously estimates the futurepredicted state of the robot, a dynamic model of the robot, and abehavioral cue model of the rider. The behavioral cue model serves toeither tune the dynamic model and/or create pseudo-measurements for roadpreview. The Kalman filter estimates the robot future state, e.g.,dynamic roll state. Once the future state is estimated, the robot pathand trajectory is planned according to the control system.

A brief overall description of the trajectory generation according tothe invention and will be given taking a leg 43 (foot 45) trajectory ofthe legged mobile robot 41 as an example. First, the aforesaid basic leg43 trajectory is generated in advance using the at least one model. Morespecifically, the trajectory is determined such that the kicking actionof the foot 45 is conducted with a robot centric coordinate systemreferenced to the body 42. The end point of a leg trajectory at the timeof foot rise from a modeled virtual ground surface (ground 55) andreferenced to the x-y-z coordinate system is computed. Then the next orsuccessive stance trajectory for that leg is planned from the model,given any high-level foot placement data (i.e., areas or regions ofground 55 that are derived from sensed or a priori data and deemed,graded, and ranked safe to support the legged mobile robot 41), and thestarting point at the time of foot fall is calculated. Based on the endand starting points, a flight leg trajectory which connects the footrise to foot fall is calculated, which provides a smooth trajectory overthe virtual ground surface and obstacles. In addition, any obstaclepresent is avoided by adding an additional clearance to the flighttrajectory as prescribed by the at least one model. As the body moves,the aforesaid coordinate system is displaced (translated and/orrotated).

In the preferred embodiment, a high-level control system is responsiblefor identifying the aforementioned footfall areas on ground 55. Sensingthe environment so each foot lands properly, path and trajectoryplanning and mission planning is performed in parallel. High-levelcontrol is input via external commands through the network interface 95,through body language of the at least one rider or passenger 101 asmeasured by the force and torque sensors 81 and IMU 82, an externalcontrol device, such as for example a radio control unit, voicecommands, or visual commands or gestures, or any combination of suchdevices and sensing. The at least one rider or passenger 101 may, forexample, pull on one side of a steering bar and shift his center ofgravity in advance or anticipation of a turn maneuver, thus cuing thelegged mobile robot 41 to begin the method of leaning into the turn andmodifying the single track path or trajectory from a straight line to acurve.

When a person rides a motorcycle, the rider looks ahead for changes inthe road, such as for example a curve or turn in the road, the riderplans the appropriate control strategy before the motorcycle reaches theturn, and the rider leans the motorcycle into the turn before the roadbegins to curve. It is this type of anticipative control strategy that alegged robot should perform if the legged robot is to operate and beridden like a motorcycle.

Because the at least one rider or passenger 101 is an important aspectof legged mobile robot 41, stabilization of the upright equilibrium orbalance in the presence of interaction between a human rider and thelegged mobile robot must be considered. The at least one rider orpassenger 101, as a control system, contributes to the stability ofbalance of the system, and to some extent the at least one rider orpassenger 101 can be used to provide cues regarding balance or full orpartial balance of legged mobile robot 41. Nevertheless, stability ofride must be maintained after an external force is applied. For thelegged mobile robot 41, this involves counteracting a pulling or pushingforce acting on the body 42. If this type of force is a severedisturbance, the legged machine can fall over due to these disturbances.Further, the legged machine cannot maintain its initial leg positions orstate and maintain stability of the upright equilibrium. A human can behurt by the robot changing leg positions or even falling over. Ahuman-friendly motion control is required, which allows the body to movenaturally coordinated with the external force and maintains a safeenvironment for the at least one rider or passenger 101. Various controlmethods exist, such as for example the LQR method for self-balancing andtracking desired position, and the reduced-order disturbance observercontrol method to estimate disturbances by external forces to generateposition references. The following discusses the decoupling andsimplification of the control paradigm to accomplish the aforementionedrequirements.

An inherent invention of the single track or in-line legged mobile robot41 is decoupling of the leg positioning along the length of the body 42or major axis of motion and the leg positioning along the width of thebody 42 or normal to major axis of motion. That is, legged vehiclesheretofore must simultaneously maintain stability of balance in thepitch and roll direction. In the preferred embodiment, the single trackor in-line legged mobile robot 41 has a defined front, rear, and sides.Thus, the single track or in-line legged mobile robot has differentoperating characteristics depending on its orientation and a preferredor major direction of motion. Whereas omnidirectional legged locomotion,and in particular sideways movement, is described thoroughly in theprior art (achieved by combined hip and knee joint movement, bringingthe body over the center of pressure of one foot, sliding the other footaway from the body, then bringing this body over the center of pressureof the other foot, and so on). Whereas it is known that the stability oflegged mobile robots, in particular legged mobile robots using bipedlocomotion, is intrinsically low. Whereas when such a bipedal robot isacted on by external forces (disturbance), its attitude easily becomesunstable. The single track or inline legged mobile robot, on the otherhand, like the motorcycle or bicycle, is inherently stable along thelength of the body 42 or major axis of motion. The single track orinline legged mobile robot maintains stability of balance in the rolldirection and (for the most part) not in the pitch direction. Thisdevice and method is highly important because it drastically simplifiescontrol for many single track or in-line legged gaits and modes ofoperation.

From the aforementioned discussion, it is necessary for the leggedmobile robot 41 to have lateral dynamic balancing, controlling attitudeon the basis of the detected inclinatory or roll angle, angularvelocity, and angular acceleration of the body 42. The walking machinemust balance so it does not roll over. Second, the walking machine mustfollow a desired trajectory. The trajectory may come from the at leastone rider or passenger 101 or path planning system. One aspect of theinvention is therefore to provide an attitude stabilization controlsystem for a legged mobile robot which enables the robot to maintain astable attitude during legged locomotion more effectively. Furthermore,once attitude destabilization causes the zero moment point to shift tonear the limit of the range within which it can exist, the attitude isrestored by correcting the walking pattern in the next step. This deviceand method is highly important because the plurality of legs along thesingle track or in-line roll axis affords a higher probability ofachieving dynamic balance in the next step, over traditional leggedlocomotion.

It is known that mathematical models have been developed for motorcycledynamics. It is known that control systems have been designed fortrajectory following and balance stabilization control. It is known thatmotion planning for the single-track system has been developed. However,none of these models were developed for walking machines, none model theability of the walking machine to take discrete footsteps, and nonemodel the different walking gaits.

Referring to FIGS. 33A-33B, the legged mobile robot 41 with the at leastone rider or passenger 101 and their center of gravity 102 is decoupledin two different subsystems. The first of these systems is an invertedpendulum system and the second is a legged system. The inverted pendulumsystem is an unstable system. The legged system is neutrally stable, andit is assumed that pitch or yaw motion is controlled separately and fordifferent control objectives than upright equilibrium or balance. It isassumed that the feet 45 are always in contact with the ground 55 andthat no slip exists. Finally, only latitudinal motion along the y-axis(perpendicular to the direction of travel, x-axis) and roll isconsidered. The latitudinal motion of the body 42 is characterized bythe projection of the center of gravity 58 to the ground 55, called thecenter of pressure 59, is measured both kinematic proprioceptively andby the filtered rate gyro and accelerometer system. The roll motion ischaracterized by the tilt angle, angle rate, and angle acceleration ofthe body 42 as measured both kinematic proprioceptively and by the IMU82. A free body diagram of a simplified model is shown in FIG. 33B. Asimple inverted pendulum model for single-track vehicle balancing uses aproportional derivative (PD) controller with a disturbance observer.

The fundamental SLIP model is a point of mass, m, and three mass-lesslegs. For clarity of presentation, FIGS. 32A-32B illustrates only oneactive leg 43. Each leg 43 is modeled by an axially elastic, laterallyrigid linear spring with a force-free length and spring constant. TheSLIP model is an equivalent rigid link and does not contain individualleg segments and joints as previously described. Locomotion dynamicsoccur in the sagittal plane with balance along the roll axis 54 in they-z plane. A full stride comprises a stance phase followed by a flightphase. The stance phase for each leg begins when the leg touches down(TD) to the ground and is elastically compressed so as to carry theweight of the body and vertical momentum force. The point of footcontact is modeled as a moment-free pin joint and remains fixed for theduration of the stance phase. The body moves forward and the leg rotatesunder the body in a clockwise fashion. The amount of weight of the bodyand vertical momentum force carried by the leg is dynamic and determinedby interaction of any other supporting legs and perturbations from theat least one rider or passenger 101 and ground. The stance phase endswhen the leg is lifted off (LO) the ground, and this begins the flightphase. During the flight phase, the leg is rotated in acounter-clockwise sense to reposition the foot ahead of the body for thenext stance phase. The flight phase ends when the leg touches down.

As will be discussed later, a leg may be momentarily lifted duringstance phase and re-positioned laterally (not sagittal) whereby themotion of the leg during flight is not counterclockwise but clockwise.Several important properties and control laws are known from prior art.Step length is the distance traveled by the foot during the stance phaseplus the distance traveled by the foot during the flight phase. Thedistance traveled by the body is the product of the product of theduration of the period and the forward speed. A forward speed methoddetermines step length. A flight duration method whereby the flightphase determines the distance traveled given constant forward speed. Astance duration method is the product of the average forward velocityand the duration of the stance phase. The above can be compared in termsof accuracy and range. Accuracy is a measure that reflects the errorbetween the desired and actual step length. Range is the differencebetween the minimum and maximum possible step length. When the walkingmachine is operating under normal conditions, the foot contact pointsare not sliding on the ground. The friction forces balance thecentrifugal force. The roll angle is computed, and the lateral forcemodeled.

Foot placement during running can be controlled by adjusting hip torqueor thrust. Using linearized step-to-step equations showed that adjustingthrust is more effective for controlling step length than adjusting hiptorque. When a mild disturbance is applied, sideways hip torque may beused to stabilize the upright equilibrium or balance and to maintain astable posture even. When a large disturbance is applied, one or morelegs 43 must be repositioned to counteract the force. The pitch angleand angular velocity of the body 42 is measured using the IMU 83combined with complementary filters and kinematic proprioceptiveinformation (body height, center of pressure, zero moment point, etc.).The angular sideways velocity and angular sideways displacement of theleg 43 are measured with rotary encoder 99. Using said feedback, thecontrol input, u, may be modeled. Furthermore, the LRQ method is knownand may be used to balance system errors with control. For example, ifthe weighting factors for the hip sideways velocity and displacement areincreased, the system becomes very sensitive to disturbance, but moreaccurate path tracking is obtained. If the weighting factors for the hipsideways velocity and displacement are increased, the system becomesless sensitive to disturbance and less accurate path tracking isobtained, requiring more leg/foot re-positioning. High weighting factorsare the preferred embodiment.

A reduced-order disturbance observer estimates the external force.However in practice, sensor noise and model mismatch prevent an exactestimate of the external force, and a thresholding control loop is usedto ignore small external forces. In other words, a thresholding controlloop is used to break the normal controllable range if a severedisturbance is applied to body 42. Such equations, from the law ofconservation of mechanical energy, are known from prior art. The body 42leans in the direction from which the external force is applied.Full-state feedback controls the stabilization of the uprightequilibrium or balance, and a reduced-order disturbance observerestimates the external force. Through the use of estimated externalforces, the hip torque and/or leg/foot repositioning occurs. Furtherrefinement of control, from the prior art, consider the steering angleand the driving torque. Insofar as a model which faithfully simulatesthe dynamics of the actual robot is created and the difference betweenthe ground reaction force of the actual robot and that of the robotmodel is controlled, the same principle can be applied with the sameeffect irrespective of the number of single track or in-line legs.

Referring to FIG. 34, research in legged locomotion has focused on thecase in which the legged system always maintains contact with theground. In the case where all three legs are in contact with the ground,as in the stance phase of a wave gait, there is an opportunity to shiftone of the legs laterally to affect balance. However, turnover of alegged vehicle can take place when the feet 45 slide or slip sideways orlaterally to a point that a normal target walking pattern cannotreestablish traction. For eliminating the drawback of the prior art, forexample, that outrigger wheels do not work over rugged and uneventerrain, the present invention provides a system for automaticallysensing and preventing turnover of single tracked or in-line leggedmobile robot by extending the at least one leg in the direction of rollto catch the fall, advancing the leg in the expected direction of motion(solving the foothold problem), and correcting the walking pattern inmid-step or in the next step. Such a device and method is highlyimportant for situations when the legged mobile robot 41 cannot bestabilized (or cued into stability of balance) by the at least one rideror passenger 101. Such a device and method is also adaptable to riderexperience, e.g., uncontrollable situations for a novice rider orpassenger may be controllable by an expert rider.

FIG. 34 is a front skeletal view illustrating the principles of thepresent invention. The legged mobile robot 41 is shown with at least oneleg 43 and foot 45 in contact with ground 55 after the feet 45 havestarted to lose traction. Uncontrolled foot slip is measured by the IMU82 and foot force and torque sensor 81. The IMU 82 senses changes in therate of body 42 roll and the foot force and torque sensor 81 senseschanges in the foot traction. As foot slip continues to increase,fraction will approach zero and rate of roll will increase measurably.The control unit 86 receives continuous measurement data from thesensors and determines via an algorithm if data inputs of slip and rateof roll are higher than achievable when feet have lateral traction withthe ground. A desired counteracting moment can be produced bycontrolling the joint actuations so as to produce a moment in thedirection of attitude restoration. In other words, a restoring forceacts to bring the inclination of the legged mobile robot closer to thatof the model. The restoring force is produced by deliberately shifting afoot away from that of the target walking pattern to shift the groundreaction forces to regain stability of balance.

It is known that as the traction of the feet 45 approaches zero (due toa slippery roadway or loose road surface, for example) the roll axis 54moves to the center of mass 58 of the body 42 as shown in FIG. 34. Thereasons that traction approaches zero (rate of roll increases) are: 1)as the feet lose traction, the leg frictional force 115 with the ground55 is now based on the coefficient of kinetic friction instead of thecoefficient of static friction; 2) friction is reduced as feet loselateral traction uncontrollably because some of the vehicle weight is ina free state; and 3) the polar moment of inertia moves to the center ofmass 103. As the legged mobile robot is rolling from an upright positionto an attitude deviating from the vertical, the normal force 114 on thefeet decreases to zero. In other words, traction approaches zero as theload transfers from the feet 45 to the free-falling center of mass 103(roll axes). It is also known that the polar moment of inertia issimultaneously reduced as the roll axis moves towards the center of mass58, allowing the legged mobile robot 41 to roll at an increased rate.

The initial condition is when the center of gravity 58 is above thesupporting point of the foot. The actuator encoders 99 measure kinematicproprioception and the IMU 82 measures body 42 displacements from thevertical reference plane 44, are compared by the control unit to make amore precise determination as to criticality of rate of roll. FIG. 21 isa simplified front view skeletal diagram illustrating the movement ofbody roll axis as foot traction approaches zero. In particular, thelegged mobile robot 41 is shown in a tilted position. When uncontrolledslip is detected, a leg in flight or near flight phase or the legcontributing least to the expected stability of the body is repositionedto catch the fall. That is in order to stabilize the legged vehicle andprevent turnover, the trajectory of the body 42 as an inverted pendulumis computed and the at least one leg, called the swing leg, is extendedin the direction of the fall. Planning of this swing leg involvescontrolling two parameters. First, FIG. 34 shows that the center ofgravity 58 trajectory is expressed as an inverted pendulum whose leglength is constant and thus defines an arc of radius R2. The center ofgravity 58 moves in a circular orbit about the supporting foot 45, andthe projected center of pressure 59 and zero moment point shifts in thedirection of the fall. Second, the expected moment of inertia of thebody 42 is calculated for the future time of when the fall would becaught, and a torque is computed to counteract the fall, which thencomputes the distance, d, required from the projected center of pressureand the swing leg arc of radius R1. The control unit 86 adjusts theplacement of the at least one foot so as to position the foot beyond theprojected center of gravity and in the direction of the roll. As aresult, a counteracting moment can be induced to obtain a large attituderestoring force, to catch the fall and prevent vehicle overturn.Simultaneously, the control unit 86 re-adjusts the gait pattern of theother legs such that in mid-step or in following footstep, the walkinggait is restored. It should be noted that the system of the presentinvention can operate on the basis of the IMU data 97 alone or thekinematic proprioception data 99 and 100 alone.

As the outstretched foot touches ground 55 and body roll is stopped, theIMU data 97 and kinematic proprioception data 99 and 100 is feed back tothe control unit 86. While the outstretched leg and foot keeps thelegged mobile robot 41 from overturning or lying down on its side, itdoes not immediately force the body 42 into an upright position. Rather,the at least one rider or passenger 101 may regain control of thevehicle while it is held at an attitude very close to that at whichcontrol was originally lost. After a predetermined pause to allow the atleast one rider or passenger 101 to regain control, the legs 43 and feet45 are repositioned through the recovery gait to raise the legged mobilerobot 41 to the fully upright position. Depending on the circumstances(e.g., based on input from kinematic proprioception and high-levelcommands), the control unit 86 is additionally programmed to slow orstop all motion and transition the legs 43 to a stable tripod stance,such that all three feet 45 are in contact with ground 55, but notnecessarily with equal force.

If the legged mobile robot 41 has come to incline greatly with respectto the maximum leg reach given the actuation time and time of fall, itis not possible to obtain a righting force to restore balance. The robottherefore falls over. In this case, the legs 43 are repositioned to asafe posture to prevent damage of the legged mobile robot and/or the atleast one rider or passenger 101. Other than for these conditions, therobot will only signal to reposition the leg far laterally in emergencysituations. Thus a cautious rider may never lose lateral traction inwhich case the system of the present invention would not becomeoperative.

Coordinated Control of Leg Trajectory Example

A brief overall description of the trajectory generation will be giventaking a leg 43 and foot 45 (shown in FIGS. 4-6) trajectory of thelegged mobile robot 41 as an example. First, the aforesaid basic leg 43trajectory is generated in advance using the at least one model. Morespecifically, the trajectory is determined such that the kicking actionof the foot 45 is conducted with a robot centric coordinate systemreferenced to the body 42. The end point of a leg trajectory at the timeof foot rise from a modeled virtual ground surface (ground 55) andreferenced to the x-y-z coordinate system is computed. Then the next orsuccessive stance trajectory for that leg is planned from the model,given any high-level foot placement data (i.e., areas or regions ofground 55 that are derived from sensed or a priori data and deemed,graded, and ranked safe to support the legged mobile robot 41), and thestarting point at the time of foot fall is calculated. Based on the endand starting points, a flight leg trajectory which connects the footrise to foot fall is calculated, which provides a smooth trajectory overthe virtual ground surface and obstacles. In addition, any obstaclepresent is avoided by adding an additional clearance to the flighttrajectory as prescribed by the at least one model. As the body moves,the aforesaid coordinate system is displaced (translated and/orrotated).

A high-level control system is responsible for identifying theaforementioned footfall areas on ground 55. Sensing the environment soeach foot lands properly, path and trajectory planning and missionplanning is performed in parallel. High-level control is input viaexternal commands through the network interface 95, through bodylanguage of the at least one rider or passenger 101 as measured by theforce and torque sensors 81 and IMU 82, an external control device, suchas for example a radio control unit, voice commands, or visual commandsor gestures, or any combination of such devices and sensing. The atleast one rider or passenger 101 may, for example, pull on one side of asteering bar and shift his center of gravity in advance or anticipationof a turn maneuver, thus cuing the legged mobile robot 41 to begin themethod of leaning into the turn and modifying the single track path ortrajectory from a straight line to a curve.

Because the at least one rider or passenger 101 is an important aspectof legged mobile robot 41, stabilization of the upright equilibrium orbalance in the presence of interaction between a human rider and thelegged mobile robot must be considered. The at least one rider orpassenger 101, as a control system, contributes to the stability ofbalance of the system, and to some extent the at least one rider orpassenger 101 can be used to provide cues regarding balance or full orpartial balance of legged mobile robot 41. Nevertheless, stability ofride must be maintained after an external force is applied. For thelegged mobile robot 41, this involves counteracting a pulling or pushingforce acting on the body 42. If this type of force is a severedisturbance, the legged machine can fall over due to these disturbances.Further, the legged machine cannot maintain its initial leg positions orstate and maintain stability of the upright equilibrium. A human can behurt by the robot changing leg positions or even falling over. Ahuman-friendly motion control is required, which allows the body to movenaturally coordinated with the external force and maintains a safeenvironment for the at least one rider or passenger 101. Various controlmethods exist, such as for example the LQR method for self-balancing andtracking desired position, and the reduced-order disturbance observercontrol method to estimate disturbances by external forces to generateposition references. The following discusses the decoupling andsimplification of the control paradigm to accomplish the aforementionedrequirements.

An inherent invention of the single track or in-line legged mobile robot41 is decoupling of the leg positioning along the length of the body 42or major axis of motion and the leg positioning along the width of thebody 42 or normal to major axis of motion. That is, legged vehiclesheretofore must simultaneously maintain stability of balance in thepitch and roll direction. In the preferred embodiment, the single trackor in-line legged mobile robot 41 has a defined front, rear, and sides.Thus, the single track or inline legged mobile robot has differentoperating characteristics depending on its orientation and a preferredor major direction of motion. Whereas omnidirectional legged locomotion,and in particular sideways movement, is described thoroughly in theprior art (achieved by combined hip and knee joint movement, bringingthe body over the center of pressure of one foot, sliding the other footaway from the body, then bringing this body over the center of pressureof the other foot, and so on). Whereas it is known that the stability oflegged mobile robots, in particular legged mobile robots using bipedlocomotion, is intrinsically low. Whereas when such a bipedal robot isacted on by external forces (disturbance), its attitude easily becomesunstable. The single track or inline legged mobile robot, on the otherhand, like the motorcycle or bicycle, is inherently stable along thelength of the body 42 or major axis of motion. The single track orinline legged mobile robot maintains stability of balance in the rolldirection and (for the most part) not in the pitch direction. Thisdevice and method is highly important because it drastically simplifiescontrol for many single track or in-line legged gates and modes ofoperation.

From the aforementioned discussion, it is necessary for the leggedmobile robot 41 to have lateral dynamic balancing, controlling attitudeon the basis of the detected inclinatory or roll angle, angularvelocity, and angular acceleration of the body 42. The mobile robot mustbalance so it does not roll over. Second, the mobile robot must follow adesired trajectory. The trajectory may come from the at least one rideror passenger 101 or path planning system. One aspect of the invention istherefore to provide an attitude stabilization control system for alegged mobile robot which enables the robot to maintain a stableattitude during legged locomotion more effectively. Furthermore, onceattitude destabilization causes the zero moment point to shift to nearthe limit of the range within which it can exist, the attitude isrestored by correcting the walking pattern in the next step. This deviceand method is highly important because the plurality of legs along thesingle track or in-line roll axis affords a higher probability ofachieving dynamic balance in the next step, over traditional leggedlocomotion.

Referring now to FIGS. 35-50, the legged mobile robot has three generalmodes of operation: 1) it is a fully autonomous mobile robot (with orwithout a passenger), 2) it is partially autonomous and remotelycontrolled through an operator control unit, and 3) it is partiallyautonomous and ridden by a human operator that communicates with therobot via body motions, verbal commands, and an interface (e.g., handlebars and handgrip controls). The operator (remote or rider) uses theoperator control unit to provide high-level steering and speed input toguide the walking machine along its path and to control the speed oftravel. The operator can also command the walking machine to turn on oroff, stand up, squat down, walk, trot, or jog. A visual display providesthe operator operational and engineering data. The operator onlyprovides high-level control input, leaving the legged mobile roboton-board control system to operate the legs, provide stability on roughterrain, and reflex responses to external disturbances. In addition, arider or passenger may partially or fully provide stability of balance.The control system responds to the at least one rider or passenger 101control: pulling and twisting of the handlebars, lateral changes ofposture, on-axis changes in posture, and momentary impulses and changesin rider or passenger posture, such as for example, back-and-forthmotion to initiate go, and backward leaning to initiate stop. When therider leans backward/forward in preparation for (i.e., a cue) adownhill/uphill slope, it causes the legged mobile robot to lower thebody height of the rear/front legs and thus optimize the projectedcenter of pressure with respect to the downhill/uphill slope. On a slopeor in advance of a slope, rider or passenger sideways leaning indicatesuprightness, and the legged mobile robot responds by adjusting footfallplacement to compensate for orientation of the body and virtual groundplane relative to the gravity vector. Subsequently, it would accommodateshallow to moderate inclines by making slight adjustments to bodyposture, while it would accommodate steep inclines by also adjusting thewalking gait pattern and using smaller steps. On level ground, sidewaysleaning would initiate body leaning for a turn.

Controlling a legged mobile robot includes sensing terrain, pathplanning, selecting footholds, and adjusting step length. Changes in leglength in response to a drop-step perturbation occur during steady statelocomotion. Goal-oriented constraints lead to improved stability. Forexample, minimizing the maximum force carried by any leg 43 whileconstraining the leg reaction force to be as close to the axis of themotion as possible. Gait heuristics are used to coordinate the legs. Forexample, legs closest to their kinematic limits in the direction ofmotion of the body may be lifted first, and legs with the largestkinematic range in the direction of motion may be placed first. Thismethod increases the probability that two legs will overlap in the nextsupport phase. Adaptability and avoidance of deadlock are emphasizedover stability by maximizing the number of legs in flight phase. Therearward legs may re-use the same footholds of the forward legs,resulting in a follow-the-leader gait.

The legged mobile robot control system must safely traverse unstructuredterrain. Three methods to afford balance by adjusting the step lengthfor uneven footholds (e.g., rough terrain) are known and include 1)maintaining constant duration of the stance and flight phases andadjusting the forward speed, 2) maintaining a constant forward runningspeed and constant duration of the stance phase and adjusting theduration of the flight phase, and 3) maintaining constant forwardrunning speed and duration of the flight phase and adjusting theduration of the stance phase. A variant of the second method is to usevertical impulse to control step length. Note that both horizontal andvertical impulse may be used to control step length, with adjustmentsmade during the flight phase. The first method of adjusting the forwardspeed gives the widest range of foothold adjustment with good accuracy,and is biologically-inspired by studies of over ground runners. Thethird method yields a small range of step lengths and is unlikely to beuseful for rough terrain locomotion. A fourth method is to place one ormore footsteps on the available footholds at the expense of stabilityand recover balance over one or more subsequent footsteps. Especially inrough terrain, isolated footholds are key to locomotion. Whilecontrolled step length adjusts the length of its steps such that thefeet land on the available footholds, forward speed, body height, andduration of ground contact must be controlled to actively balance thewalking machine while traversing rough terrain. Being configured in theforegoing three methods, the embodiment is able to generate a gait witha high margin of stability even on uneven terrain and in othersituations where ground contact is made with two or more planessimultaneously. The legged mobile robot control system must also accountfor mechanical losses in the system while safely traversing unstructuredterrain.

The operation of the legged mobile robot 41 according to the inventionwill now be explained primarily with reference to gait (leggedlocomotion model or pattern) generation. A number of candidate footfallpositions are established beforehand, one of the candidates is selectedand the target walking pattern model (gait) is used during the controlcycles of each walking step. Then a desired trajectory for the body 42is computed using heuristic and simulation algorithms to select thepattern of footholds from the set of reachable footholds that best matchthe desired trajectory, afford balance, and minimize the dynamicmomentum for lateral and roll axes. At least one gait model is stored inROM 88 comprising a clock-driven model of the support and swing orflight phases of a gait.

Referring again to FIGS. 35-50, FIG. 35 is an example of a gait model(diagram) illustrating a wave gait comprising a 10/11 support (beta)phase (black horizontal line) and 1/11 swing (no line) phases along thehorizontal axis (one complete cycle or gait) for each of the three legs43 (a, b, and c correspond to legs 43 a, 43 b and 43 c, respectively)shown on the vertical axis, for the single track or in-line three leggedmobile robot 41. The first diagram shall now be explained as an examplefor all of the gait model diagrams. From clock 0 to 10, the front leg 45a is on ground 55 and traveling rearward with respect to body 42. Fromclock 10 to 11 (the clock is reset at 11), the front leg 45 a is in theair swinging or in flight forward with respect to body 42. From clock 0to 5, the middle leg 45 b is on ground 55 and traveling rearward withrespect to body 42. From clock 5 to 6, the middle leg 45 b is in the airswinging or in flight forward with respect to body 42. From clock 6 to11 (the clock is reset to 0 at 11), the rear leg 45 b is on ground 55and traveling rearward with respect to body 42. From clock 0 to 1, therear leg 45 c is in the air swinging or in flight forward with respectto body 42. From clock 1 to 11 (the clock is reset to 0 at 11), the rearleg 45 c is on ground 55 and traveling rearward with respect to body 42.Generally, the velocity of the leg 43 and hence foot 45 during the swingor flight phase is faster than the velocity of the body 42. Generally, along stance with respect to swing (large beta) reflects a slow body 42velocity, as the forward swing typically occurs at maximum leg velocityto maximize ground support and stability of balance. It is called a wavegait because the flight phase of the legs progresses from the rear tomiddle to front leg 43. In this example, the backward swing is evenlydispersed over the gait period. FIG. 36 is an example of a wave gaitmodel for the single track or in-line three legged mobile robot 41 witha 5/6 stance (beta) and 1/6 flight phasing. FIG. 37 is an example of awave gait model for the single track or in-line three legged mobilerobot 41 with a 2/3 stance (beta) and 1/3 flight phasing. Note at clocks4 and 8 there may be a make before break or break before make transitionbetween the middle and rear leg support and first and middle legsupport, respectively. FIG. 38 is an example of a wave gait model forthe single track or in-line three legged mobile robot 41 with a 5/6stance (beta) and 1/6 flight phasing where the swing cycles are groupedtogether. FIG. 39 is an example of a wave gait model for the singletrack or in-line three legged mobile robot 41 with a 8/11 stance (beta)and 3/11 flight phasing with two intervals where all three legs aresimultaneously supporting the body 42. This wave gait closely resemblesa trot gait. Trotting is running at a rapid speed, and pacing is runningat constant speed. FIG. 40 is an example of an equal phase wave gaitmodel for the single track or in-line three legged mobile robot 41. Noteat clock 6 there may be a make before break or break before maketransition between the first and rear leg support. FIG. 41 is an exampleof a variation on an equal phase backward wave gait model for the singletrack or in-line three legged mobile robot 41. This gait uses thedynamic momentum of the body 42 to afford balance. A brief (one-clock)support period allows all three legs to maintain the general stability,forward speed, and direction of travel of the body. As a model, thecharacteristics required (forward velocity, variation in body height,etc.) to implement the gait are also stored in ROM 88. FIG. 42 is anexample of a variation on an equal phase wave gait model for the singletrack or in-line three legged mobile robot 41. This is an example of atrot or pace gait wherein two legs provide pitch stability during onehalf of the gait period and dynamic momentum of the body 42 provides theother half. FIG. 43 is an example of a variation of a 2/3 stance and 1/3flight wave gait for the single track or in-line three legged mobilerobot 41, wherein affordance is given to reposition the middle legduring the front and rear leg support. Note at clock 0 there may be amake before break or break before make transition between the first andrear leg support. FIG. 44 is an example of a variation of a 2/3 stanceand 1/3 flight backward and forward wave gait for the single track orin-line three legged mobile robot 41, wherein affordance is given toreposition the middle leg to accommodate changes in front and rear legstance. Note at clocks 2, 4, 8, and 10 there may be a make before breakor break before make transition between the first and rear leg support.FIG. 45 is an example of a running/leaping gait combined with a hoppingmodel for the single track or in-line three legged mobile robot 41. Themiddle leg provides the vertical hopping force and front and rear legsprovide both vertical hopping force and pitch stability during landingof the body 42. Hopping, bounding, leaping, running, and jumping arecharacterized by periods wherein all feet leave the ground and the body42 is in ballistic flight. Legged robots that use a ballistic flightphase, called dynamic legged robots, because leg extension directlyaffects forward momentum. Such a gait may be used in rugged terrainwhere only one foothold exists to support the body 42. Hopping,bounding, leaping, running, and jumping gaits may be interleaved withthe aforementioned walking, trotting, and pacing gaits. Such ability ofmotion affords the legged machine to traverse terrain that is toodifficult for comparable wheeled and tracked machines. FIG. 46 is anexample of a running gait for the single track or in-line three leggedmobile robot 41. FIG. 47 is an example of a pronking gait for the singletrack or in-line three legged mobile robot 41. Pronking is jumping withall three legs simultaneously followed by a period where the body 42 isin ballistic flight.

Referring again to FIGS. 48-50, FIG. 48 is an example of a bounding gaitfor the single track or in-line three legged mobile robot 41. The gaitis repeated twice for clarity. Bounding is jumping wherein the front,middle, and back legs alternately touch the ground. For bounding, themiddle leg extends to the point of first overlap and the rear leg to themaximum forward extent for jumping. By positioning the feet in a widestance, as opposed to an in-line or single-track stance, both legscontribute to the jumping force and stability is afforded in the rolland yaw axis with the first leg responsible for the pitch and yawcontrol. A series of adjustments in step length are required to arriveat a suitable takeoff point and correct leg states for leaping andjumping. The legs must be in a state to impart a vertical impulse to theground such that the dynamic momentum of the body affords balance atlanding. A vertical impulse is the integral of the vertical forceexerted on the ground during the stance phase, determines the durationof the flight phase, and determines the length of each step (givenconstant forward velocity). As such, the legs must not be at maximumextension. FIG. 49 is a top and side skeletal view of the single trackor in-line three legged mobile robot illustrating an example of abounding takeoff (left to right). While airborne, the front leg extendsto anticipate the first point of overlap and the middle leg becomesfully extended forward for landing. FIG. 50 is a top and side skeletalview of the single track or in-line three legged mobile robotillustrating a bounding landing (left to right). Note how in bothtakeoff and landing a bipedal-like stance may be used to maintainstability of balance in the roll axis.

While the invention has thus been shown and described with reference tothe specific embodiments, it will be apparent to those skilled in theart that various changes, modifications, and improvements may be madewithout departing from the scope and spirit of the invention.Accordingly it is to be understood that the invention is not limited bythe scope of the illustrative embodiment or to the details of thedescribed arrangements. For example, the present invention has beenshown and described as being a three legged robot. However, the designand method of the present invention is also applicable to an articulatedbody structure for a multi-legged walking robot having two, three, fouror more in-line legs. In another example, the single track or in-linelegs may be adapted for movement on the surface of or through water. Inanother example, while many of the embodiments were shown and describedwith reference to straight line motion, the invention also enablestrajectories for various curved motion and situations, including curvedtrajectory stair climbing and descent. In another example, while many ofthe embodiments were shown and described with reference to a foot-basedsensor for determining the foot and leg forces and torques and motorencoders for leg position and orientation, the invention is not limitedto this type of control and sensing. In another example, while many ofthe embodiments were shown and described with respect to application ofmodels and other a priori data set in advance, this is not limitativeand the invention can also be applied in cases where the control valuesduring locomotion are calculated completely in real time. Moreover,while invention was shown and described with reference to a leggedmobile robot, the invention can not only be applied to other types ofmobile robots, but can also be applied to various stationary industrialrobots. Furthermore, the invention can also be applied to movableobjects other than robots.

What is claimed is:
 1. A method of operating a single track leggedvehicle having a body and at least three in-line legs aligned one behindthe other, the method comprising: controlling each in-line leg of thesingle track vehicle to coordinate movement of the in-line legs along adesired single-track trajectory where each in-line leg attaches at itsproximal end to a frame of the body of the vehicle arrangedsubstantially parallel to a major axis of the frame and theforward/backward direction of travel of the vehicle, each in-line leghas a foot at its distal end, and the in-line attachment of the legs tothe body results in a center of gravity and a center of pressure thatare directly in line with the legs when the legs are simply extendedstraight down from the body, resulting in inherent instability along anaxis, the coordinated movement controlled by causing each in-line leg toselectively perform a stance-to-flight phase, a flight phase, aflight-to-stance phase, and a stance phase wherein: controlling, duringthe stance-to-flight phase of a corresponding in-line leg, includingcontrolling foot movement that unloads reaction forces and torquesbetween the foot of the corresponding in-line leg and the ground suchthat the foot of the corresponding in-line leg is lifted off the ground;controlling, during the flight phase of the corresponding in-line leg,includes controlling leg movement that maintains an upright position ofthe body and that moves the foot of the corresponding in-line leg in thesame general direction and at a generally faster rate as a majordirection of motion of the body; controlling, during theflight-to-stance phase of the corresponding in-line leg, includescontrolling foot positioning that places the foot of the correspondingin-line leg on the ground according to the desired single-tracktrajectory wherein reaction forces and torques are developed between thefoot and the ground; and controlling, during the stance phase of thecorresponding in-line leg, includes controlling foot force and torquesuch that foot-to-ground interaction develops reaction forces andtorques that are transferred from the foot through the correspondingin-line leg to propel, torque, and stabilize the body in the x, y, z,pitch, roll, and yaw axes; and transitioning each in-line leg betweenthe stance to flight phase, the flight phase, the flight to stance phaseand the stance phase to propel and torque the body along three axesaccording to the desired single-track trajectory.
 2. The method of claim1, further comprising: receiving sensed data from at least oneaccelerometer mounted to the vehicle and at least one gyroscope mountedto the vehicle; utilizing the sensed data to determine velocity,acceleration, attitude and gravitational forces; and utilizing thedetermined velocity, acceleration, attitude and gravitational forces inthe control of at least one of the flight-to-stance phase, flight phase,stance-to-flight phase and stance phase.
 3. The method of claim 1,wherein: controlling foot movement during the stance-to-flight phasecomprises controlling at least one of: foot position, movement, force,torque, extension velocity and acceleration, and retraction velocity andacceleration; controlling leg movement during a flight phase comprisescontrolling at least one of: in-line leg movement and foot trajectory;controlling foot positioning during the flight-to-stance phase comprisescontrolling at least one of: foot position, movement, force, torque,extension velocity and acceleration, and retraction velocity andacceleration; and controlling foot force and torque during the stancephase comprises controlling at least one of: foot position, movement,force, torque, extension velocity and acceleration, and refractionvelocity and acceleration.
 4. The method of claim 1, further comprising:performing predictive control of the in-line legs to propel and torquethe body along three axes according to the desired single-tracktrajectory by: measuring frame speed and acceleration vectors, center ofmass coordinates, and ground contact duration for each foot; dynamicallyadjusting the length, force, and torque of the in-line legs to achieve aset of expected values according to the desired single-track trajectory;continually determining deviations from the expected values; andcompensating for the deviations to achieve active balance of the leggedvehicle.
 5. The method of claim 1, further comprising: decouplingpositioning of the in-line legs along a length of the body frompositioning of the in-line legs along the width of the body and parallelto the ground; and controlling stability of balance of the vehicle overtime in the roll direction.
 6. The method of claim 1, further comprisingperforming for each in-line leg: selecting a target walking patternmodel from a plurality of walking pattern models, wherein each targetwalking pattern includes a clock-driven model of the stance and flightphases for each in-line leg; computing the desired single-tracktrajectory for the body of the vehicle using at least one of a heuristicalgorithm and a simulation algorithm; and selecting a pattern offootholds from a set of reachable footholds that most closely correspondto the desired single-track trajectory, and which minimize dynamicmomentum for lateral and roll axes; and utilizing dynamic momentum tomaintain the desired single-track trajectory during periods ofsingle-leg support and double-leg support.
 7. The method of claim 1,wherein controlling each in-line leg of the vehicle further comprises:controlling each of the at least three in-line legs of the vehicle bycontinually sensing body attitude and roll angle throughout each of thestance to flight phase, the flight phase, the flight to stance phase andthe stance phase.
 8. The method of claim 1, wherein controlling eachin-line leg of the vehicle comprises: performing the flight to stancephase for a select in-line leg by: accelerating the foot of the selectin-line leg backward and along the curved single-track trajectory beforecontact with the ground, until the foot is generally stationary withrespect to the ground, and then making contact with the ground todevelop any ground reaction forces and torques; and by: performing thestance to flight phase for a select in-line leg by: generallymaintaining the foot stationary with respect to the ground while thefoot is being unloaded of any ground reaction forces and torques; toperform a desired single-track turn maneuver.
 9. The method of claim 1,wherein controlling each in-line leg of the vehicle comprises:controlling at least one in-line leg so as to position the foot of thecontrolled in-line leg to a select side of the projected center ofgravity on to the ground to develop, during a stance phase, groundreaction forces that are generally normal to the major direction ofmotion and ground reaction torques in the pitch, roll, and/or yaw axisto maintain stability of balance along a desired single tracktrajectory.
 10. The method of claim 9, wherein controlling each in-lineleg of the vehicle comprises: positioning the landing foot offset fromthe foot lifting off according to a pre-programmed strategy forstability of balance along the desired single-track trajectory.
 11. Themethod of claim 1, wherein controlling each in-line leg of the vehiclecomprises: controlling the length of the in-line legs during anassociated stance phase of each in-line leg so as to be differentbetween feet of the in-line legs positioned on, to the right of, or tothe left of the projected center of gravity of the body on to the groundto level the body attitude, within a working range of the in-line legsand their feet.
 12. The method of claim 1, wherein controlling eachin-line leg of the vehicle comprises: controlling two of the in-linelegs to transition from stance-to-flight and flight-to-stance phase in agenerally make before break fashion such that both feet support thebody, the landing foot is placed spatially apart from the foot liftingoff, for stability of balance in the pitch axis along a desired singletrack trajectory.
 13. The method of claim 1, further comprising:defining, for each in-line leg, a corresponding spatial volume thatlimits possible in-line foot placement, each spatial volume constrainedbased upon pitch and roll movement at a hip joint that joins acorresponding in-line leg to the body, and based upon extension andretraction of the corresponding in-line leg by knee and ankle joints ofthe in-line leg; and controlling each in-line leg according to a legmotion model to operate each in-line leg within its defined spatialvolume such that pairs of feet corresponding to pairs of in-line legshave sufficient reach and movement range in length, width and height,relative to the body, to be placed in a bipedal stance, with respect tothe major axis and major direction of motion and travel, the combinedground reaction forces between two feet during a stance phase so as toimpart at least one of: a torque to rotate the body in the pitch, roll,and/or yaw axis; and a force to propel the body in at least one of thex, y, and z axes.
 14. The method of claim 1, further comprising:defining, for each in-line leg, a corresponding spatial volume thatlimits possible in-line foot placement, each spatial volume constrainedbased upon pitch and roll movement at a hip joint that joins acorresponding in-line leg to the body, and based upon extension andretraction of the corresponding in-line leg by knee and ankle joints ofthe in-line leg; and controlling each in-line leg according to a legmotion model to operate each in-line leg within its defined spatialvolume such that three feet corresponding to three in-line legs havesufficient reach and movement range in length, width and height,relative to the body, to be placed in a tripedal stance, with respect tothe major axis and major direction of motion and travel, the combinedground reaction forces between three feet during a stance phase so as toimpart at least one of: a torque to rotate the body in the pitch, roll,and/or yaw axis; and a force to propel the body in at least one of thex, y, and z axes.
 15. The method of claim 1, further comprisingreceiving feedback and control signals from an operator interfacesystem, in communication with the control system, wherein the operatorinterface feedback and control signals provide at least steering angle,throttle and braking control signals to the control system to enable theoperator to control stability of balance in the roll axis of thevehicle.
 16. The method of claim 1, wherein controlling each in-line legof the vehicle comprises: controlling the at least three in-line legsaccording to an elastic-mechanical and dynamical model to compute footposition of each in-line leg to maintain body stability along a desiredsingle track trajectory.
 17. The method of claim 16, wherein controllingeach in-line leg of the vehicle comprises: controlling at least twoin-line legs by inducing select ones of roll, pitch and yaw torquesbetween the foot of a corresponding in-line leg and the ground and/or atleast two in-line legs by selectively inducing roll, pitch and yawtorques between each foot of the at least two controlled in-line legsand the ground to control a body trajectory along a desired single-tracktrajectory.
 18. The method of claim 16, further comprising: predictingan elastic deformation of at least one leg when in support with theground to maintain desired ground reaction forces and torques to controla body trajectory along a desired single-track trajectory.
 19. Themethod of claim 16, wherein the body comprises a segmented frame, themethod further comprising: computing segmented frame joint angles in atleast one axis between adjacent ones of the in-line legs to groundundulations and to the curvature of a single track turn maneuver with aminimally narrow profile relative to the major axis of motion; anddynamically adjusting the length, force, and torque of the in-line legsto maintain body stability based upon the computations.
 20. The methodof claim 16, wherein the body comprises a segmented frame, the methodfurther comprising: computing elastic energy storage and releasecomponents between frame segments and in the in-line legs, wherein theelastic components operate in at least one axis, wherein the elasticcomponents store and release kinetic energy for transfer between bodysegments and in-line legs; and dynamically adjusting the length, force,and torque of the in-line legs to maintain body stability based upon thecomputations.
 21. The method of claim 16, wherein the body comprises asegmented frame, the method further comprising: computing dynamicmomentum forces and torques developed by moving frame segments andcorresponding ones of the in-line legs relative to each other, whereinthe components operate in at least one axis; and dynamically adjustingthe length, force, and torque of the in-line legs to maintain bodystability based upon the computations.
 22. The method of claim 16,wherein controlling each in-line leg of the vehicle comprises:performing the flight phase for a select in-line leg by: computingdynamic momentum forces and torques developed by moving a in-line leg inflight phase, wherein the components operate in at least one axis; anddynamically adjusting the center of mass of a select one of the in-linelegs in the flight phase to maintain body stability by: sweeping aselect in-line leg inward or outward normal to the body and majordirection of travel; and reducing or extending at least one of a lengthof the select in-line leg and a corresponding position of the center ofmass of the select in-line leg; so as to impart a desired torque in thepitch, roll and/or yaw axis to maintain stability of balance along thedesired single-track trajectory.
 23. The method of claim 1, furthercomprising: controlling the single track vehicle to operate autonomouslyregardless of at least steering angle and throttle control signals tosense and prevent turnover while enabling normal riding techniques inall but out of control situations.
 24. The method of claim 1, whereincontrolling each in-line leg of the vehicle comprises: controlling eachin-line leg so as to vary the length of each in-line leg with respect tothe average body height during a stance phase such that the body isstable in height, roll, and pitch over uneven ground.
 25. The method ofclaim 1, wherein controlling each in-line leg of the vehicle comprises:controlling the in-line legs so as to incline the body in the pitch axisto lower a front of the body and raise a back of the body when ascendinga gradient; controlling the in-line legs so as to recline in the pitchaxis to raise the front of the body and lower the back of the body whendescending the gradient; and controlling the in-line legs so as to rollthe body in the roll axis when traversing a gradient normal to the majordirection of travel; within the working range of the in-line legs andtheir feet.
 26. The method of claim 1, wherein controlling each in-lineleg of the vehicle comprises: positioning the foot of the forward mostin-line leg to control the trajectory of the single-track path by:placing a second foot corresponding to a second one of the in-line legsin proximity of a first foot corresponding to a first one of the in-linelegs; placing a third foot corresponding to a third one of the in-linelegs in proximity of the second foot; and repeating positioning thefirst foot, placing the second foot, and placing the third foot suchthat each foot follows a desired single-track trajectory.